Atkore (ATKR) 10-K16 Nov 232023 FY Annual reportFinancial data

Company Profile

Cover

Cover - USD ($) $ in Billions	12 Months Ended
Cover - USD ($) $ in Billions	Sep. 30, 2023	Nov. 14, 2023	Mar. 31, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2023
Current Fiscal Year End Date	--09-30
Document Transition Report	false
Entity File Number	001-37793
Entity Registrant Name	Atkore Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	90-0631463
Entity Address, Address Line One	16100 South Lathrop Avenue
Entity Address, City or Town	Harvey
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60426
City Area Code	708
Local Phone Number	339-1610
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	ATKR
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Document Financial Statement Error Correction [Flag]	false
Entity Public Float			$ 5.2
Entity Common Stock, Shares Outstanding		37,318,097
Documents Incorporated by Reference	Portions of the registrant's proxy statement to be filed with the United States Securities and Exchange Commission in connection with the registrant's 2024 annual meeting of stockholders (the "Proxy Statement") are incorporated by reference into Part III hereof. Such Proxy Statement will be filed within 120 days of the registrant's fiscal year ended September 30, 2023.
Entity Central Index Key	0001666138
Document Fiscal Year Focus	2023
Amendment Flag	false
Document Fiscal Period Focus	FY

Audit Information

Audit Information	12 Months Ended
Audit Information	Sep. 30, 2023
Audit Information [Abstract]
Auditor Name	DELOITTE & TOUCHE LLP
Auditor Location	Chicago, Illinois
Auditor Firm ID	34

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Net sales	$ 3,518,761	$ 3,913,949	$ 2,928,014
Cost of sales	2,179,260	2,273,924	1,802,401
Gross profit	1,339,501	1,640,025	1,125,613
Selling, general and administrative	388,206	370,044	293,019
Intangible asset amortization	57,804	36,176	33,644
Operating income	893,491	1,233,805	798,950
Interest expense, net	35,232	30,676	32,899
Loss on extinguishment of debt	0	0	4,202
Other (income) and expense, net	7,969	(490)	(18,152)
Income before income taxes	850,290	1,203,620	780,001
Income tax expense	160,391	290,186	192,144
Net income	$ 689,899	$ 913,434	$ 587,857
Net income per share
Basic (in dollars per share)	$ 17.51	$ 20.56	$ 12.38
Diluted (in dollars per share)	$ 17.27	$ 20.30	$ 12.19

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 689,899	$ 913,434	$ 587,857
Other comprehensive (loss) income, net of tax:
Change in foreign currency translation adjustment	10,212	(23,943)	2,385
Change in unrecognized (loss) income related to pension benefit plans	5,994	2,523	11,443
Total other comprehensive (loss) income	16,206	(21,420)	13,828
Comprehensive income	$ 706,105	$ 892,014	$ 601,685

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Current Assets:
Cash and cash equivalents	$ 388,114	$ 388,751
Accounts receivable, less allowance for current and expected credit losses of $5,179 and $2,544, respectively	559,854	528,904
Inventories, net	493,852	454,511
Prepaid expenses and other current assets	96,670	80,654
Total current assets	1,538,490	1,452,820
Property, plant and equipment, net	559,041	390,220
Intangible assets, net	394,372	382,706
Goodwill	311,106	289,330
Right-of-use assets, net	120,747	71,035
Deferred income taxes	546	9,409
Other long-term assets	10,707	3,476
Total Assets	2,935,009	2,598,996
Current Liabilities:
Accounts payable	292,734	244,100
Income tax payable	6,322	5,521
Accrued compensation and employee benefits	45,576	61,273
Customer liabilities	121,576	99,447
Lease obligations	16,230	13,789
Other current liabilities	82,166	77,781
Total current liabilities	564,604	501,911
Long-term debt	762,687	760,537
Long-term lease obligations	105,517	57,975
Deferred income taxes	22,346	15,640
Other long-term liabilities	11,736	13,146
Total Liabilities	1,466,890	1,349,209
Equity:
Common stock, $0.01 par value, 1,000,000,000 shares authorized, 37,317,893 and 41,351,350 shares issued and outstanding, respectively	374	415
Treasury stock, held at cost, 0 and 260,900 shares, respectively	0	(2,580)
Additional paid-in capital	506,783	500,117
Retained earnings	994,902	801,981
Accumulated other comprehensive loss	(33,940)	(50,146)
Total Equity	1,468,119	1,249,787
Total Liabilities and Equity	$ 2,935,009	$ 2,598,996

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Statement of Financial Position [Abstract]
Accounts receivable, allowance for current and expected credit losses	$ 5,179	$ 2,544
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	37,317,893	41,351,350
Common stock, shares outstanding (in shares)	37,317,893	41,351,350
Treasury stock (in shares)	0	260,900

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net income	$ 689,899	$ 913,434	$ 587,857
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	115,524	84,415	78,557
Amortization of debt issuance costs and original issue discount	2,151	2,151	2,497
Deferred income taxes	12,860	3,054	(43,306)
Loss on extinguishment of debt	0	0	4,202	$ 273
Provision for losses on accounts receivable and inventory	5,269	10,235	645
Stock-based compensation expense	21,101	17,245	17,047
Amortization of right-of-use assets	20,321	13,916	14,515
Other adjustments to net income	7,481	4,850	(208)
Changes in operating assets and liabilities, net of effects from acquisitions
Accounts receivable	(30,278)	17,749	(219,659)
Inventories	(42,419)	(160,980)	(81,544)
Prepaid expenses and other current assets	(11,152)	(21,718)	(6,462)
Accounts payable	32,298	(28,968)	98,444
Income taxes	(3,088)	(92,802)	80,291
Accrued and other liabilities	(10,176)	27,198	63,459
Other, net	(2,157)	(2,944)	(23,433)
Net cash provided by operating activities	807,634	786,835	572,902
Investing activities
Capital expenditures	(218,888)	(135,776)	(64,474)
Insurance proceeds for properties, plant and equipment	0	0	9,627
Proceeds from sale of properties, plant and equipment	123	779	81
Acquisitions of businesses, net of cash acquired	(83,385)	(307,805)	(43,195)
Net cash used for investing activities	(302,150)	(442,802)	(97,961)
Financing activities
Repayments of short-term debt	0	0	(4,000)
Issuance of long-term debt	0	0	798,000
Repayments of long-term debt	0	0	(835,120)
Issuance of common stock, net of taxes withheld	(14,428)	(24,045)	2,660
Repurchase of common stock	(491,033)	(500,161)	(135,066)
Payments for debt financing costs and fees	0	0	(10,930)
Finance lease payments	(1,320)	0	0
Net cash used for financing activities	(506,781)	(524,206)	(184,456)
Effects of foreign exchange rate changes on cash and cash equivalents	661	(7,365)	1,333
Increase (decrease) in cash and cash equivalents	(637)	(187,538)	291,818
Cash and cash equivalents at beginning of period	388,751	576,289	284,471
Cash and cash equivalents at end of period	388,114	388,751	576,289	$ 284,471
Supplementary Cash Flow information
Interest paid	43,670	30,529	23,726
Income taxes paid, net of refunds	150,934	379,769	155,114
Capital expenditures, not yet paid	7,893	8,653	1,094
Acquisitions of businesses, not yet paid	13,625	12,628	0
Operating cash flows from cash paid on operating lease liabilities	15,155	12,549	13,035
Operating lease right-of-use assets obtained in exchange for lease liabilities	$ 63,644	$ 38,794	$ 13,538

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Sep. 30, 2020		47,407
Balance at beginning of period at Sep. 30, 2020	$ 378,410	$ 475	$ (2,580)	$ 487,223	$ (64,154)	$ (42,554)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	587,857				587,857
Other comprehensive income (loss)	13,828					13,828
Stock-based compensation	17,047			17,047
Issuance of common stock, net of shares withheld for tax (in shares)		918
Issuance of common stock, net of shares withheld for tax	2,660	$ 9		2,651
Repurchase of common stock (in shares)		(2,328)
Repurchase of common stock	(135,066)	$ (23)			(135,043)
Ending balance (in shares) at Sep. 30, 2021		45,997
Balance at end of period at Sep. 30, 2021	864,736	$ 461	(2,580)	506,921	388,660	(28,726)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	913,434				913,434
Other comprehensive income (loss)	(21,420)					(21,420)
Stock-based compensation	17,245			17,245
Issuance of common stock, net of shares withheld for tax (in shares)		434
Issuance of common stock, net of shares withheld for tax	(24,045)	$ 4		(24,049)
Repurchase of common stock (in shares)		(5,080)
Repurchase of common stock	(500,161)	$ (51)			(500,113)
Ending balance (in shares) at Sep. 30, 2022		41,351
Balance at end of period at Sep. 30, 2022	1,249,787	$ 415	(2,580)	500,117	801,981	(50,146)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	689,899				689,899
Other comprehensive income (loss)	16,206					16,206
Stock-based compensation	21,101			21,101
Issuance of common stock, net of shares withheld for tax (in shares)		288
Issuance of common stock, net of shares withheld for tax	(14,432)	$ 3		(14,435)
Repurchase of common stock (in shares)		(4,322)
Repurchase of common stock	(494,442)	$ (43)			(494,399)
Retirement of Treasury Stock	0		2,580		(2,580)
Ending balance (in shares) at Sep. 30, 2023		37,317
Balance at end of period at Sep. 30, 2023	$ 1,468,119	$ 375	$ 0	$ 506,783	$ 994,901	$ (33,940)

BASIS OF PRESENTATION AND SUMMA

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	1. BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of presentation Organization and Ownership Structure — Atkore Inc. (the “Company” or “Atkore”) is a leading manufacturer of Electrical products primarily for the non-residential construction and renovation markets and Safety & Infrastructure for the construction and industrial markets. The Electrical segment manufactures high quality products used in the construction of electrical power systems including conduit, cable, and installation accessories. The Safety & Infrastructure segment designs and manufactures solutions including metal framing, mechanical pipe, perimeter security, and cable management for the protection and reliability of critical infrastructure. The Company was incorporated in the State of Delaware on November 4, 2010 under the name Atkore International Group Inc. As of September 20, 2022, Atkore was the sole stockholder of Atkore International Holdings Inc. (“AIH”), which in turn was the sole stockholder of Atkore International Inc. (“AII”). On December 28, 2022, AIH merged into AII, with AII being the surviving entity. Accordingly, Atkore is now the sole stockholder of AII. Holders of common stock are entitled to cast one vote for each share held of record on all matters submitted to a vote of the stockholders. Additionally, holders of common stock are entitled to receive, on a pro rata basis, dividends and distributions, if any, that the Company’s board of directors may declare out of legally available funds. Share Repurchase Program — On February 5, 2019, the board of directors approved a share repurchase program, under which the Company may repurchase up to $50.0 million of its outstanding common stock. As of December 25, 2020, there were no authorized repurchases remaining on that program. On January 28, 2021, the board of directors approved a share repurchase program, under which the Company may repurchase up to $100.0 million of its outstanding common stock. As of September 30, 2021, there were no authorized repurchases remaining. On November 16, 2021, the board of directors approved a share repurchase program, under which the Company may repurchase up to $400 million of its outstanding common stock. On April 26, 2022, the board of directors approved an amendment to the aforementioned plan, extending it to a total repurchase of the Company’s outstanding common stock of up to $800.0 million. On November 11, 2022, the board of directors approved an amendment to the aforementioned plan, extending it to a total repurchase authorization of the Company’s outstanding stock of $1,300 million. As of September 30, 2023, $309.1million of repurchases remained available under the plan. Basis of Presentation — The accompanying audited consolidated financial statements of the Company and all of its subsidiaries included herein have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The audited consolidated financial statements include the assets and liabilities used in operating the Company's business. All intercompany balances and transactions have been eliminated in consolidation. The results of companies acquired or disposed of are included in the audited consolidated financial statements from the effective date of acquisition or up to the date of disposal. Fiscal Periods — The Company has a fiscal year that ends on September 30. The Company's fiscal quarters typically end on the last Friday in December, March and June as it follows a 4-5-4 calendar. Use of Estimates — The preparation of the consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclose contingent assets and liabilities at the date of the consolidated financial statements and report the associated amounts of revenues and expenses. Actual results could differ materially from these estimates. Summary of significant accounting policies Revenue Recognition — The Company’s revenue arrangements primarily consist of a single performance obligation to transfer promised goods which is satisfied at a point in time when title, risks and rewards of ownership, and subsequently control have transferred to the customer. This generally occurs when the product is shipped to the customer, with an immaterial amount of transactions in which control transfers upon delivery. The Company primarily offers assurance-type standard warranties that do not represent separate performance obligations. Under the Inflation Reduction Act of 2022 (“IRA”), the Company is eligible for tax credits related to the manufacturing and selling of components used in the solar energy industry, starting on January 1, 2023. These tax credits are transferable under the IRA when they meet certain criteria. When credits do not meet the transferability criteria, the benefit is recognized within income tax expense in accordance with ASC 740, “Income Taxes.” The Company concluded that the tax credits earned during fiscal 2023 are not transferable and as a result, the Company recognized the benefit of the fiscal 2023 tax credits in its income tax expense. The Company has contractual arrangements with some customers who purchase credit eligible components to transfer a portion of these tax credits to those customers. In instances where the Company has such arrangements, and the credits are not transferable, the Company may transfer the economic value of the agreed upon portion of the tax credits in a manner agreed upon between the Company and the customer. Pursuant to such contractual arrangements, if the tax credits are eligible for transfer and will be transferred to the customer, the Company identifies two separate performance obligations under these contracts with the first being to transfer the promised goods and the second being to transfer the defined portion of the tax credits earned. The Company allocates the total value of these transactions between the two performance obligations. As a result of this allocation, the Company recognizes a reduction to revenue, similar to a rebate. When the Company does not transfer credits but instead transfers only the economic value, there is only a single performance obligation to transfer the promised goods with transfer of the economic value of the credits recognized as a reduction of revenue. The solar tax credit receivable is recorded in Prepaid Expenses and Other Current Assets whereas the liability to transfer the defined portion of the tax credits or the economic value is recorded in Customer Liabilities. For the year ended September 30, 2023, the Company has recognized a reduction of revenue of $30,401 for the economic value of tax credits to be transferred and a year to date benefit to income tax expense of $39,493. As of September 30, 2023, the Company has a $30,401 liability for credits to be transferred or the economic value of the credits and a solar tax credit receivable of $39,493. As of September 30, 2023, all activity related to the solar tax credits is within the Safety & Infrastructure segment. The Company has certain arrangements that require it to estimate at the time of sale the amounts of variable consideration that should not be recorded as revenue as certain amounts are not expected to be collected from customers, as well as an estimate of the value of products to be returned. The Company principally relies on historical experience, specific customer agreements, and anticipated future trends to estimate these amounts at the time of sale and to reduce the transaction price. These arrangements include sales discounts and allowances, volume rebates, and returned goods. The Company records its obligations related to these items within the Customer Liabilities line on the balance sheet. The Company has elected to utilize certain practical expedients available under GAAP. The Company records amounts billed to customers for reimbursement of shipping and handling costs within revenue. Shipping and handling costs associated with outbound freight after control over a product has transferred to a customer are accounted for as fulfillment costs and are included in cost of sales. Sales taxes and other usage-based taxes are excluded from revenue. The practical expedient not to disclose information about remaining performance obligations has also been elected as these obligations have an original duration of one year or less. The Company does not evaluate whether the selling price includes a financing interest component for contracts that are less than a year. The Company also expenses costs incurred to obtain a contract, primarily sales commissions, as all obligations will be settled in less than one year. The Company typically receives payment 30 to 60 days from the point it has satisfied the related performance obligation. See Note 17, “Segment Information” for revenue disaggregated by geography and product categories. Cost of Sales — The Company includes all costs directly related to the production of goods for sale in cost of sales in the statement of operations. These costs include direct material, direct labor, production related overheads, excess and obsolescence costs, lower of cost or market provisions, freight and distribution costs, and the depreciation and amortization of assets directly used in the production of goods for sale. Selling, General and Administrative Expenses — These amounts primarily include payroll-related expenses for both administrative and selling personnel, compensation expense from stock-based awards, restructuring-related charges, third-party professional services and transactional gains or losses for foreign currency transactions, excluding the foreign exchange exposure for intercompany loan transactions, which is included in Other (income) and expense, net. Cash and Cash Equivalents — The Company considers all highly liquid investments with a maturity of three months or less, when purchased, to be cash equivalents. Accounts Receivable and Allowance for current and expected credit losses — The Company carries its accounts receivable at their face amounts less an allowance for current and expected credit losses. The allowance for current and expected credit losses reflects the best estimate of current and expected losses inherent in the Company’s accounts receivable portfolio determined on the basis of historical experience, specific allowances for known troubled accounts and other available evidence. Inventories — Inventories are recorded at the lower of cost (primarily LIFO) or market value. The Company estimates losses for excess and obsolete inventory through an assessment of its net realizable value based on the aging of the inventory and an evaluation of the likelihood of recovering the inventory costs based on anticipated demand and selling price. See Note 10, “Inventories, net.” Property, Plant and Equipment — Property, plant and equipment, net, is recorded at cost less accumulated depreciation. Maintenance and repair expenditures are charged to expense when incurred. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets as follows: Buildings 4 to 40 years Building improvements 3 to 20 years Machinery and equipment 1 to 20 years Leasehold improvements Lesser of remaining term of the lease or useful life Software 2 to 10 years The internal and external costs incurred to develop internal use computer software during the application development stage of the implementation, including the design of the chosen path, are capitalized. Other costs, including expenses incurred during the preliminary project stage, training expenses, data conversion costs and expenses incurred in the post implementation stage are expensed in the period incurred. Capitalized costs are amortized ratably over the useful life of the software when the software becomes operational. Upgrades and enhancements to internal use software are capitalized only if the costs result in additional functionality. The Company does not plan to sell or market its internal use computer software to third parties. Business Combinations — The Company accounts for business combinations using the acquisition method of accounting, which requires that once control is obtained, all the assets acquired and liabilities assumed, including amounts attributable to noncontrolling interests, are recorded at their respective fair values at the date of acquisition. The determination of fair values of identifiable assets and liabilities requires estimates and the use of valuation techniques when market value is not readily available. For intangible assets acquired in a business combination, the Company typically use the income method. Significant estimates in valuing certain intangible assets include, but are not limited to, the amount and timing of future cash flows, growth rates, discount rates and useful lives. The excess of the purchase price over fair values of identifiable assets and liabilities is recorded as goodwill. Long-Lived Asset and Finite - Lived Intangible Asset Impairments — The Company reviews long-lived assets, including property, plant and equipment and finite-lived intangible assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of the asset may not be fully recoverable. The Company groups assets at the lowest level for which cash flows are separately identified in order to measure an impairment. Recoverability of an asset or asset group is first measured by a comparison of the carrying amount to its estimated undiscounted future cash flows expected to be generated by the asset or asset group. If the carrying amount exceeds its estimated undiscounted future cash flows, an impairment charge is recognized as the amount by which the carrying amount of the asset or asset group exceeds the estimated fair value. If impairment is determined to exist, any related impairment loss is calculated based on the estimated fair value. Impairment losses on assets to be disposed of or held for sale, if any, are based on the estimated proceeds to be received, less costs of disposal. The Company also considers potential impairment indicators associated with other finite-lived intangible assets, including its customer relationships, patents, and non-compete agreements. An impairment is recognized if the carrying value of an asset or asset group exceeds the estimated undiscounted future cash flows expected to result from the use of the asset or asset group and its eventual disposition. The Company's key customers are primarily wholesale and national distributors. The terms of these relationships are based on purchase orders and are not contractually based. Customer relationships are amortized on a straight-line basis over their useful lives, ranging from 6 to 14 years. The Company evaluates the appropriateness of remaining useful lives based on customer attrition rates. Other intangible assets are amortized on a straight-lined basis over their estimated useful lives, ranging from 1 to 20 years. The Company did not have a triggering event during fiscal 2023, 2022 and 2021. Goodwill and Indefinite-Lived Intangible Asset Impairments — The Company assesses the recoverability of goodwill and indefinite-lived trade names on an annual basis in accordance with Accounting Standards Codification (“ASC”) 350 “Intangibles - Goodwill and Other.” The measurement date is the first day of the fourth fiscal quarter, or more frequently, if events or circumstances indicate that it is more likely than not that the fair value of a reporting unit or the respective indefinite-lived trade name is less than the carrying value. The Company can elect to perform a quantitative or qualitative test of impairment. For fiscal 2023, 2022, and 2021 the Company performed a quantitative impairment assessment for goodwill. The Company calculated the fair value of its six reporting units considering three valuation approaches: (a) the income approach; (b) the guideline public company method; and (c) the comparable transaction method. The income approach calculates the fair value of the reporting unit using a discounted cash flow approach. Internally forecasted future cash flows, which the Company believes reasonably approximate market participant assumptions, are discounted using a weighted average cost of capital (Discount Rate) developed for each reporting unit. The Discount Rate is developed using market observable inputs, as well as considering whether or not there is a measure of risk related to the specific reporting unit’s forecasted performance. The key uncertainties in these calculations are the assumptions used in determining the reporting unit’s forecasted future performance, including revenue growth and EBITDA margins, as well as the perceived risk associated with those forecasts. Fair value under the guideline public company method is determined for each reporting unit by applying market multiples for comparable public companies to the reporting unit’s financial results. Fair value under the comparable transaction method is determined based on exchange prices in actual transactions and on asking prices for controlling interests in public or private companies currently offered for sale by applying market multiples for comparable public companies to the unit’s financial results. The key uncertainties in the guideline public company method and the comparable transaction method calculations are the assumptions used in determining the reporting unit's comparable public companies, comparable transactions and the selection of the market multiples. As a result of the Company’s plans to exit its operations in Russia and expectation to sell the related business at a loss, the Company recognized a goodwill impairment of $1,721 that was allocated from the reporting unit on a relative fair value basis. With the exception of the impairment recorded to the expected sale of the Russia operations, the Company did not record any other goodwill impairments in fiscal 2023, 2022, and 2021. As noted above, ASC 350 also requires that the Company test the indefinite-lived intangible assets for impairment at least annually. Under ASC 350, if the carrying value of the indefinite-lived asset is higher than its fair value, then the asset is deemed to be impaired and the impairment charge is estimated as the excess carrying value over the fair value. The Company calculated the fair value of its indefinite-lived intangible assets using the income approach, specifically the relief-from-royalty method. The relief-from-royalty method is used to estimate the cost savings that accrue to the owner of an intangible asset who would otherwise have to pay royalties or license fees on revenues earned through the use of the asset. Internally forecasted revenues, which the Company believes reasonably approximate market participant assumptions, are multiplied by a royalty rate to arrive at the estimated net after tax cost savings. The royalty rate used in the analysis is based on an analysis of empirical, market-derived royalty rates for guideline intangible assets. The net after tax cost savings are discounted using the Discount Rate. The Discount Rate is developed using market observable inputs, as well as considering whether or not there is a measure of risk related to the specific indefinite lived intangible assets' forecasted performance. The key uncertainties in these calculations are the assumptions used in determining the revenue associated with each indefinite-lived intangible asset and the royalty rate. The Company did not record any indefinite-lived asset impairments in fiscal 2023, 2022, and 2021. Fair Value Measurements — Authoritative guidance for fair value measurements establishes a three-level hierarchy that ranks the quality and reliability of information used in developing fair value estimates. The hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. In cases where two or more levels of inputs are used to determine fair value, a financial instrument's level is determined based on the lowest level input that is considered significant to the fair value measurement in its entirety. The three levels of the fair value hierarchy are summarized as follows: Level 1-inputs are based upon quoted prices (unadjusted) in active markets for identical assets or liabilities which are accessible as of the measurement date. Level 2-inputs are based upon quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and model-derived valuations for the asset or liability that are derived principally from or corroborated by market data for which the primary inputs are observable, including forward interest rates, yield curves, credit risk and exchange rates. Level 3-inputs for the valuations are unobservable and are based on management's estimates of assumptions that market participants would use in pricing the asset or liability. The fair values are therefore determined using model-based techniques such as option pricing models and discounted cash flow models. Income Taxes and Uncertain Tax Positions — The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities using enacted tax rates in effect for the year it is expected the differences will reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period of the enactment date. The Company periodically assesses the realizability of the deferred tax assets. In making this determination management considers all available evidence, both positive and negative, including earnings history, expectations of future taxable income and available tax planning strategies. A valuation allowance is recorded to reduce the Company’s deferred tax assets to the amount that is considered more likely than not to be realized. Changes in the required valuation allowance are recorded in income in the period such determination is made. Certain tax positions may be considered uncertain requiring an assessment of whether an allowance should be recorded. Provisions for uncertain tax positions provide a recognition threshold based on an estimate of whether it is more likely than not that a position will be sustained upon examination. The Company measures its uncertain tax positions as the largest amount of benefit that is greater than a 50% likelihood of being realized upon examination. Interest and penalties related to unrecognized tax benefits are recorded as a component of income tax expense. See Note 7, “Income Taxes.” On December 22, 2017, “H.R.1,” also known as the Tax Cuts and Jobs Act (“TCJA”) was signed into law. As part of the enactment of TCJA, the Company recorded a global intangible low-taxed income (“GILTI”) provision for the first time beginning in fiscal 2019. The GILTI provision of TCJA requires certain income earned by controlled foreign corporations (“CFCs”) to be included currently in the gross income of the CFCs controlling U.S. shareholder. In accordance with accounting standards applicable to income taxes, there is allowed an accounting policy choice of either (1) treating taxes due on U.S. inclusions in taxable income related to GILTI as a current period expense when incurred (the “period cost method”) or (2) factoring such amounts into the Company’s measurement of its deferred taxes (the “deferred method”). The Company has elected the period method. On August 16, 2022, the Inflation Reduction Act of 2022 (“IRA”) was enacted into law. The IRA contains significant tax law changes, including a corporate alternative minimum tax of 15% on adjusted financial statement income, which if applicable for the Company would be effective beginning October 1, 2023, a 1% excise tax on stock repurchases after December 31, 2022, and various tax incentives which include, but are not limited to, credits related to the manufacturing and selling of components used in the solar energy industry which took effect on January 1, 2023. The Company has recognized the benefit of credits related to the manufacturing and selling of components used in the solar energy industry in the income tax provision as described in the previous section discussing Revenue Recognition. Leases — Starting in fiscal 2020, as a result of the adoption of ASC 842 “Leases,” the Company recognizes if an arrangement is a lease at the inception of the contract. The Company determines which party has the right to control an asset during the contract term and recognizes a Right of Use (“ROU”) asset and lease obligations based on the present value of the future minimum lease payments over the term of the lease. Refer to Note 2, “Leases” for further discussion of the Company’s accounting policy for leases. Translation of Foreign Currency — For the Company's non-U.S. subsidiaries that report in a functional currency other than United States dollars, assets and liabilities are translated into United States dollars using period end exchange rates. Revenue and expenses are translated at the monthly average exchange rates in effect during the reporting period. Foreign currency translation adjustments are included as a component of accumulated other comprehensive loss within the consolidated statements of comprehensive income. Recent Accounting Pronouncements Atkore has not adopted any accounting standards in the current fiscal year. There are no accounting standards with adoption dates in the next fiscal year that are applicable to the Company.

LEASES

LEASES	12 Months Ended
LEASES	Sep. 30, 2023
Leases [Abstract]
LEASES	2. LEASES The Company engages in leasing transactions to meet the needs of the business. The Company leases certain manufacturing facilities, warehouses and distribution centers, office space, forklifts, vehicles and other machinery and equipment. The determination to lease, rather than purchase, an asset is primarily contingent upon capital requirements, duration of the forecasted business investment, and asset availability. The Company determines if an arrangement is a lease at inception and all arrangements deemed to be leases are subject to an assessment to determine the classification between finance and operating leases. The Company's significant assumptions and judgments in determining whether a contract is or contains a lease include establishing whether the supplier has the ability to use other assets to fulfill its service or whether the terms of the agreement enable the Company to control the use of a dedicated property, plant and equipment asset during the contract term. In the majority of the Company's contracts where it must identify whether a lease is present, it is readily determinable that the Company controls the use of the assets and obtains substantially all of the economic benefit during the term of the contract. In those contracts where identification is not readily determinable, the Company has determined that the supplier has either the ability to use another asset to provide the service or the terms of the contract give the supplier the rights to operate the asset at its discretion during the term of the contract, in which case the arrangement would not constitute a lease. Right-of-use assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term as of the commencement date. The Company’s lease agreements have terms that include both lease and non-lease components. Lease component fees are included in the present value of future minimum lease payments. Conversely, non-lease components are not subject to capitalization and are expensed as incurred. Per ASC 842 “Leases,” the contractual interest rate is used to calculate the present value of the future minimum lease payments. However, the majority of the Company’s leases do not provide an implicit rate. Therefore, the Company's significant assumption and judgments in determining the discount rate include determining the incremental borrowing rate. The Company’s incremental borrowing rates are based on the term of the lease, the economic environment of the lease and the effect of collateralization. The valuation of the ROU asset also includes lease payments made in advance of the lease commencement date and initial direct costs incurred to secure the lease and is reduced for lease incentives. The lease terms include options to extend or terminate the lease when it is reasonably certain the Company will exercise the options. Leases with an initial term of 12 months or less are classified as short-term leases and are not recorded on the consolidated balance sheets. The lease expense for short-term leases is recognized on a straight-line basis over the lease term. The Company has certain leasing agreements, related to leased vehicles available to our sales personnel, that contain guaranteed residual value terms, which are not expected to be triggered. The Company’s leasing portfolio does not contain any material restrictive covenants. Leases (in thousands) September 30, 2023 September 30, 2022 Assets Operating lease assets $ 117,966 $ 68,715 Finance lease assets 7,108 5,209 Right-of-use assets, at cost $ 125,074 $ 73,924 Less: accumulated amortization (4,327) (2,889) Right-of-use assets, net $ 120,747 $ 71,035 Liabilities Current liabilities: Current portion of operating lease liabilities $ 15,030 $ 12,777 Current portion of finance lease liabilities 1,200 1,012 Current lease obligations $ 16,230 $ 13,789 Noncurrent liabilities: Operating lease liabilities $ 104,047 $ 56,601 Finance lease liabilities 1,470 1,374 Long-term lease obligations $ 105,517 $ 57,975 Total lease obligations $ 121,747 $ 71,764 Lease Cost The following table summarizes lease costs by type of cost for the fiscal year ended September 30, 2023, and the fiscal year ended September 30, 2022. In the consolidated statements of operations, cost of sales and selling, general and administrative expenses included lease costs of $20,054 and $7,215 for the fiscal year ended September 30, 2023 and $15,583 and $3,732 for the fiscal year ended September 30, 2022. Fiscal year ended (in thousands) September 30, 2023 September 30, 2022 Amortization of right-of-use assets $ 21,540 $ 13,916 Interest on lease liabilities 131 71 Variable lease costs 3,146 2,471 Short term lease costs 2,451 2,857 Total lease costs $ 27,269 $ 19,315 Maturity of Lease Liabilities The Company's maturity analysis of its lease liabilities as of September 30, 2023 is as follows: (in thousands) Financing Leases Operating Leases 2024 $ 1,369 $ 21,471 2025 1,003 19,557 2026 578 17,913 2027 131 16,026 2028 4 12,811 2029 and after — 54,418 Total lease payments $ 3,085 $ 142,195 Less: Interest (415) (23,118) Present value of lease liabilities $ 2,670 $ 119,077 Lease Term and Discount Rate Fiscal year ended September 30, 2023 September 30, 2022 Weighted-average remaining lease term (years) Operating leases 9.5 8.1 Finance leases 2.5 2.7 Weighted-average discount rate Operating leases 6.4 % 4.5 % Finance leases 4.6 % 3.0 %
LEASES	2. LEASES The Company engages in leasing transactions to meet the needs of the business. The Company leases certain manufacturing facilities, warehouses and distribution centers, office space, forklifts, vehicles and other machinery and equipment. The determination to lease, rather than purchase, an asset is primarily contingent upon capital requirements, duration of the forecasted business investment, and asset availability. The Company determines if an arrangement is a lease at inception and all arrangements deemed to be leases are subject to an assessment to determine the classification between finance and operating leases. The Company's significant assumptions and judgments in determining whether a contract is or contains a lease include establishing whether the supplier has the ability to use other assets to fulfill its service or whether the terms of the agreement enable the Company to control the use of a dedicated property, plant and equipment asset during the contract term. In the majority of the Company's contracts where it must identify whether a lease is present, it is readily determinable that the Company controls the use of the assets and obtains substantially all of the economic benefit during the term of the contract. In those contracts where identification is not readily determinable, the Company has determined that the supplier has either the ability to use another asset to provide the service or the terms of the contract give the supplier the rights to operate the asset at its discretion during the term of the contract, in which case the arrangement would not constitute a lease. Right-of-use assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term as of the commencement date. The Company’s lease agreements have terms that include both lease and non-lease components. Lease component fees are included in the present value of future minimum lease payments. Conversely, non-lease components are not subject to capitalization and are expensed as incurred. Per ASC 842 “Leases,” the contractual interest rate is used to calculate the present value of the future minimum lease payments. However, the majority of the Company’s leases do not provide an implicit rate. Therefore, the Company's significant assumption and judgments in determining the discount rate include determining the incremental borrowing rate. The Company’s incremental borrowing rates are based on the term of the lease, the economic environment of the lease and the effect of collateralization. The valuation of the ROU asset also includes lease payments made in advance of the lease commencement date and initial direct costs incurred to secure the lease and is reduced for lease incentives. The lease terms include options to extend or terminate the lease when it is reasonably certain the Company will exercise the options. Leases with an initial term of 12 months or less are classified as short-term leases and are not recorded on the consolidated balance sheets. The lease expense for short-term leases is recognized on a straight-line basis over the lease term. The Company has certain leasing agreements, related to leased vehicles available to our sales personnel, that contain guaranteed residual value terms, which are not expected to be triggered. The Company’s leasing portfolio does not contain any material restrictive covenants. Leases (in thousands) September 30, 2023 September 30, 2022 Assets Operating lease assets $ 117,966 $ 68,715 Finance lease assets 7,108 5,209 Right-of-use assets, at cost $ 125,074 $ 73,924 Less: accumulated amortization (4,327) (2,889) Right-of-use assets, net $ 120,747 $ 71,035 Liabilities Current liabilities: Current portion of operating lease liabilities $ 15,030 $ 12,777 Current portion of finance lease liabilities 1,200 1,012 Current lease obligations $ 16,230 $ 13,789 Noncurrent liabilities: Operating lease liabilities $ 104,047 $ 56,601 Finance lease liabilities 1,470 1,374 Long-term lease obligations $ 105,517 $ 57,975 Total lease obligations $ 121,747 $ 71,764 Lease Cost The following table summarizes lease costs by type of cost for the fiscal year ended September 30, 2023, and the fiscal year ended September 30, 2022. In the consolidated statements of operations, cost of sales and selling, general and administrative expenses included lease costs of $20,054 and $7,215 for the fiscal year ended September 30, 2023 and $15,583 and $3,732 for the fiscal year ended September 30, 2022. Fiscal year ended (in thousands) September 30, 2023 September 30, 2022 Amortization of right-of-use assets $ 21,540 $ 13,916 Interest on lease liabilities 131 71 Variable lease costs 3,146 2,471 Short term lease costs 2,451 2,857 Total lease costs $ 27,269 $ 19,315 Maturity of Lease Liabilities The Company's maturity analysis of its lease liabilities as of September 30, 2023 is as follows: (in thousands) Financing Leases Operating Leases 2024 $ 1,369 $ 21,471 2025 1,003 19,557 2026 578 17,913 2027 131 16,026 2028 4 12,811 2029 and after — 54,418 Total lease payments $ 3,085 $ 142,195 Less: Interest (415) (23,118) Present value of lease liabilities $ 2,670 $ 119,077 Lease Term and Discount Rate Fiscal year ended September 30, 2023 September 30, 2022 Weighted-average remaining lease term (years) Operating leases 9.5 8.1 Finance leases 2.5 2.7 Weighted-average discount rate Operating leases 6.4 % 4.5 % Finance leases 4.6 % 3.0 %

ACQUISITIONS

ACQUISITIONS	12 Months Ended
ACQUISITIONS	Sep. 30, 2023
Business Combination and Asset Acquisition [Abstract]
ACQUISITIONS	3. ACQUISITIONS From time to time, the Company enters into strategic acquisitions in an effort to better service existing customers and to attain new customers. Fiscal 2023 On November 7, 2022, Atkore HDPE, LLC, a wholly-owned subsidiary of the Company, acquired the assets of Elite Polymer Solutions (“Elite”), for a purchase price of $90,230, of which $75,981 was paid at closing and an additional purchase price payable of $14,000 was accrued, of which $500 was paid in fiscal 2023 subsequent to the acquisition date. Elite is a manufacturer of high density polyethylene (HDPE) conduit, primarily serving the telecommunications, utility, and transportation markets. As a result of the acquisition, the Company preliminarily recognized $18,669 of tax deductible goodwill, $68,480 of identifiable intangible assets, of which $68,200 relates to customer relationships with an estimated useful life of 8 years, and $3,082 of working capital and other net tangible assets. The Company finalized the purchase price allocation of Elite in the fourth quarter of fiscal 2023. The acquisition in fiscal 2023 was funded using cash-on-hand. The Company incurred approximately $968 in acquisition-related expenses for fiscal 2023, which was recorded as a component of selling, general and administrative expenses. Net sales and net income of the above acquisition are included in the condensed consolidated financial statement of operations for the post-acquisition period. Due to the immaterial nature of this acquisition, the Company did not include the pro forma results of operations for this acquisition for the current period or the previous interim period. Fiscal 2022 On August 31, 2022, Atkore International Inc., and Atkore HDPE, LLC, wholly-owned subsidiaries of the Company, acquired the outstanding stock of two separate, but related, companies doing business as Cascade Poly Pipe & Conduit (“Cascade”) and Northwest Polymers, for a total purchase price of $62,100, of which $52,738 was paid at closing and an additional purchase price payable of $9,362 was accrued. Cascade is a manufacturer specializing in smooth wall HDPE conduit made from recycled materials, primarily serving the telecommunications, utility and datacom markets. Northwest Polymers is a leading recycler of PVC, HDPE and other plastics and a strategic supply partner to Cascade and other manufacturers. The Company finalized the purchase price allocation of these companies in the third quarter of fiscal 2023. On June 22, 2022, Atkore International Inc., a wholly-owned subsidiary of the Company acquired all of the outstanding stock of United Poly Systems, LLC (“United Poly”), for a purchase price of $227,420. United Poly is a manufacturer of high density polyethylene (“HDPE”) pressure pipe and conduit, primarily serving the telecommunications, water infrastructure, renewables and energy markets. The Company finalized the purchase price allocation of United Poly in the third quarter of fiscal 2023. On May 19, 2022, Allied Tube and Conduit Corporation, wholly-owned subsidiary of the Company acquired the assets of Talon Products, LLC (“Talon”), for a purchase price of $4,193. Included in Talon’s purchase price is a purchase price payable of $402. Talon is a manufacturer of non-metallic, injection molded cable cleats, primarily serving the power distribution markets. The Company finalized the purchase price allocation of Talon in the fourth quarter of fiscal 2022. On December 21, 2021, Atkore HDPE, LLC and Allied Tube and Conduit Corporation, wholly-owned subsidiaries of the Company, acquired the assets of Four Star Industries LLC (“Four Star”), for a purchase price of $23,195. Four Star is a manufacturer of HDPE conduit, primarily serving the telecommunications, utility, infrastructure and datacom markets. The Company finalized the purchase price allocation of Four Star in the third quarter of fiscal 2022. On December 20, 2021, Columbia-MBF Inc., a wholly-owned subsidiary of the Company acquired all of the outstanding stock of Sasco Tubes & Roll Forming Inc. (“Sasco”), for a purchase price of $16,184, of which $13,320 was paid at closing and an additional purchase price payable of $2,864 was accrued. Sasco is a Canadian manufacturer of metal framing and related products serving the electrical, mechanical, construction and solar industries. The Company finalized the purchase price allocation of Sasco in the third quarter of fiscal 2022. The acquisitions in fiscal 2022 were funded using cash-on-hand. The Company incurred approximately $3,424 in acquisition-related expenses for these acquisitions, which were recorded as a component of selling, general and administrative expenses. The purchase price was allocated to tangible and intangible assets acquired and liabilities assumed, based on their fair values. The following table summarizes the Level 3 fair values assigned to the net assets acquired and liabilities assumed as of the acquisition date for fiscal 2022: (in thousands) United Poly Other Total Fair value of consideration transferred: Cash consideration $ 227,420 $ 93,044 $ 320,464 Purchase price payable — 12,628 12,628 Working Capital Adjustment — 668 668 Total consideration transferred $ 227,420 $ 106,340 $ 333,760 Fair value of assets acquired and liabilities assumed: Cash 11,514 126 11,640 Accounts receivable 23,679 9,291 32,970 Inventories 13,455 8,111 21,566 Intangible assets 128,840 54,330 183,170 Fixed assets 13,648 8,533 22,181 Accounts payable (11,940) (5,086) (17,026) Income taxes (15,542) (2,075) (17,617) Other (2,751) 245 (2,506) Net assets acquired 160,903 73,475 234,378 Excess purchase price attributed to goodwill acquired $ 66,517 $ 32,865 $ 99,382 The Company estimates $31.1 million of the goodwill recognized by the fiscal 2022 acquisitions is deductible for tax purposes, $11.7 million that relates to United Poly and $19.4 million that relates to Cascade and Northwest Polymer. The Company estimates Goodwill recognized from the acquisitions in fiscal 2022 consists largely of the synergies and economies of scale from integrating this company with existing businesses. The following table summarizes the fair value of intangible assets as of the acquisition date: United Poly Other (in thousands) Fair Value Weighted Average Useful Life (Years) Fair Value Weighted Average Useful Life (Years) Customer relationships $ 111,700 11 $ 50,020 9 Other 17,140 8 4,310 8 Total intangible assets $ 128,840 $ 54,330 The following table presents unaudited pro forma results of operations for the Company and all companies acquired in fiscal 2022 as if those acquisitions had occurred on October 1, 2020. The results presented below are for the fiscal years ended: Fiscal year ended (in thousands) September 30, 2022 September 30, 2021 Pro forma net sales $ 4,060,993 $ 3,048,378 Pro forma net income 920,022 584,754 The pro forma condensed financial information is presented for illustrative purposes only and does not indicate the actual financial results of the Company if the closing of the acquisitions in the current year had been completed on October 1, 2020, nor is it indicative of the results of operations in future periods. Included in the unaudited pro forma financial information for the years ended September 30, 2022 and September 30, 2021 were pro forma adjustments to reflect the results of operations of the acquisitions in the current year as though those acquisitions were completed as of October 1, 2020, as well as the impact of amortizing certain acquisition accounting adjustments such as amortizable intangible assets. The pro forma financial information neither indicates the impact of possible business model changes nor considers any potential impact of current market conditions, expense efficiencies or other factors. Net sales and net income of the acquired companies are included in the consolidated statement of operations for the year ended September 30, 2022 for the post-acquisition period. Fiscal 2021 On February 24, 2021, Atkore Southwest, LLC, a wholly-owned subsidiary of the Company acquired the assets of FRE Composites USA Inc. and separately the Company acquired all of the outstanding stock of FRE Composites Inc., collectively described as FRE Composites Group (“FRE Composites”), for a purchase price of $36,993, net of cash received. FRE Composites is a leading manufacturer of fiberglass conduit for the electrical and industrial market. The purchase price was allocated to tangible and intangible assets acquired and liabilities assumed, based on their fair values. On October 22, 2020, Atkore Plastics Southeast, LLC, a wholly-owned subsidiary of the Company acquired the assets of Queen City Plastics, Inc. (“Queen City Plastics”), a leading manufacturer of PVC conduit, elbows and fittings for the electrical market. The purchase price was allocated to tangible assets acquired and liabilities assumed based on their fair values. The purchase price of $6,214 was deemed immaterial to the Company. The acquisitions in fiscal 2021 were funded using cash-on-hand. The Company incurred approximately $667 in acquisition-related expenses for these acquisitions, which were recorded as a component of selling, general and administrative expenses. The purchase price for FRE Composites, which was finalized during the fourth quarter of fiscal 2021, was allocated to tangible and intangible assets acquired and liabilities assumed, based on their fair values. The following table summarizes the Level 3 fair values assigned to the net assets acquired and liabilities assumed as of the acquisition date for fiscal 2021: (in thousands) FRE Composites Fair value of consideration transferred: Cash consideration $ 36,993 Fair value of assets acquired and liabilities assumed: Cash 437 Accounts receivable 2,163 Inventories 3,355 Intangible assets 18,300 Fixed assets 8,509 Accounts payable (1,186) Income Taxes (4,293) Other (240) Net assets acquired 27,045 Excess purchase price attributed to goodwill acquired $ 9,948 The Company estimates $1.6 million of the goodwill recognized from the FRE Composites acquisition is deductible for tax purposes. The goodwill consists largely of the synergies and economies of scale from integrating FRE Composites with existing businesses. The following table summarizes the fair value of intangible assets as of the acquisition date: FRE Composites ($ in thousands) Fair Value Weighted Average Useful Life (Years) Customer relationships $ 14,700 12.0 Other 3,600 6.0 Total intangible assets $ 18,300

POSTRETIREMENT BENEFITS

POSTRETIREMENT BENEFITS	12 Months Ended
POSTRETIREMENT BENEFITS	Sep. 30, 2023
Retirement Benefits [Abstract]
POSTRETIREMENT BENEFITS	4. POSTRETIREMENT BENEFITS The Company has a number of non-contributory and contributory defined benefit retirement plans covering certain United States employees. Net periodic pension benefit cost is based on periodic actuarial valuations that use the projected unit credit method of calculation and is charged to the statements of operations on a systematic basis over the expected average remaining service lives of current participants. The benefits under the defined benefit plans are based on various factors, such as years of service and compensation. For all periods presented, all defined pension benefit plans are frozen, whereby participants no longer accrue credited service. The net periodic cost for the periods presented was as follows: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Interest cost $ 5,175 $ 2,958 $ 2,729 Expected return on plan assets (5,027) (5,392) (6,424) Amortization of actuarial loss 667 631 1,327 Net periodic cost $ 815 $ (1,803) $ (2,368) The weighted-average assumptions used to determine net periodic pension cost during the period were as follow: September 30, 2023 September 30, 2022 September 30, 2021 Discount rate 5.4 % 2.7 % 2.5 % Expected return on plan assets 5.0 % 4.0 % 6.2 % Rate of compensation increase N/a N/a N/a The change in the benefit obligations, plan assets and the amounts recognized on the consolidated balance sheets was as follows (in thousands): Change in benefit obligations: Balance as of September 30, 2021 $ 140,745 Interest cost 2,958 Actuarial loss (36,411) Benefits and administrative expenses paid (6,090) Balance as of September 30, 2022 101,202 Interest cost 5,175 Actuarial gain (4,882) Benefits and administrative expenses paid (6,165) Balance as of September 30, 2023 $ 95,330 Change in plan assets: Balance as of September 30, 2021 $ 138,056 Actual return on plan assets (28,230) Employer contributions 188 Benefits and administrative expenses paid (6,090) Balance as of September 30, 2022 103,925 Actual return on plan assets 7,463 Employer contributions 220 Benefits and administrative expenses paid (6,165) Balance as of September 30, 2023 $ 105,443 Funded status: Funded status as of September 30, 2022 $ 2,723 Funded status as of September 30, 2023 $ 10,113 (in thousands) September 30, 2023 September 30, 2022 Amounts recognized in the consolidated balance sheets consist of: Pension Non-Current Assets $ 10,113 $ 2,723 Pension liabilities — — Net amount recognized $ 10,113 $ 2,723 Amounts recognized in accumulated other comprehensive loss (before income taxes) consist of: Net actuarial loss $ (15,631) $ (23,616) Total loss recognized $ (15,631) $ (23,616) Weighted-average assumptions used to determine pension benefit obligations at year end: Discount rate 5.8 % 5.4 % Rate of compensation increase N/a N/a The following table summarizes the defined benefit pension plans with accumulated benefit obligations in excess of plan assets: (in thousands) September 30, 2023 September 30, 2022 Accumulated benefit obligation $ — $ — Fair value of plan assets — — Neither plan had accumulated benefit obligations in excess of plan assets as of September 30, 2022. The following table summarizes the defined benefit pension plans with projected benefit obligations in excess of plan assets: (in thousands) September 30, 2023 September 30, 2022 Projected benefit obligation $ — $ — Fair value of plan assets — — Neither plan had projected benefit obligations in excess of plan assets as of September 30, 2022. In determining the expected return on plan assets, the Company considers the relative weighting of plan assets by class, historical performance of asset classes over long-term periods, asset class performance expectations as well as current and future economic conditions. The Company’s investment strategy for its pension plans is to manage the plans on a going-concern basis. Current investment policy is to minimize risk in the plan assets for the purpose of enhancing the security of benefits for participants. For the pension plans, this policy targets a 100% allocation to debt securities. As of September 30, 2023, the 46% of plan assets held in cash and cash equivalents is a result of timing differences as the Company continues to move to the target allocation of 100% debt securities. Pension plans have the following weighted-average asset allocations: Asset Category: September 30, 2023 September 30, 2022 Equity securities —% 50% Debt securities 54% 46% Cash and cash equivalents 46% 4% Total 100% 100% The Company evaluates its defined benefit plans’ asset portfolios for the existence of significant concentrations of risk, such as investments in a single entity, industry, foreign country and individual fund manager. As of September 30, 2023, there were no significant concentrations of risk in the Company’s defined benefit plan assets. The Company’s plan assets are accounted for at fair value and are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value of assets and their placement within the fair value hierarchy levels. The Company’s asset allocations are presented in the table below: September 30, 2023 September 30, 2022 (in thousands) Level 1 Level 2 Total Level 1 Level 2 Total United States equity securities $ — $ — $ — $ 29,583 $ — $ 29,583 Non-U.S. equity securities — — — 22,913 — 22,913 Fixed income securities 21,119 35,733 56,852 22,639 24,794 47,433 Cash and cash equivalents 48,591 — 48,591 3,996 — 3,996 Total $ 69,710 $ 35,733 $ 105,443 $ 79,131 $ 24,794 $ 103,925 Equity securities consist primarily of publicly traded United States and non-U.S. equities. Publicly traded securities are valued at the last trade or closing price reported in the active market in which the individual securities are traded. Certain equity securities are held within commingled funds, which are valued at the unitized net asset value (“NAV”) or percentage of the NAV as determined by the custodian of the fund. These values are based on the fair value of the underlying net assets owned by the fund. Fixed income securities consist primarily of government and agency securities, corporate debt securities, and mortgage and other asset-backed securities. When available, fixed income securities are valued at the closing price reported in the active market in which the individual security is traded. Government and agency securities and corporate debt securities are valued using the most recent bid prices or occasionally the mean of the latest bid and ask prices when markets are less liquid. Asset-backed securities including mortgage-backed securities are valued using broker/dealer quotes when available. When quotes are not available, fair value is determined by utilizing a discounted cash flow approach, which incorporates other observable inputs such as cash flows, underlying security structure and market information including interest rates and bid evaluations of comparable securities. As of September 30, 2023 and September 30, 2022, the Company did not have any Level 3 pension assets. Certain fixed income securities are held within commingled funds, which are valued utilizing NAV as determined by the custodian of the fund. These values are based on the fair value of the underlying net assets owned by the fund. Cash and cash equivalents consist primarily of short-term commercial paper, and other cash or cash-like instruments including settlement proceeds due from brokers, stated at cost, which approximates fair value. Transfers between levels of the fair value hierarchy are recognized on the actual date of the event or circumstance giving rise to the transfer, which generally coincides with the Company’s valuation process. Contribution amounts are determined and funded based on laws and regulations and with the assistance of professionally qualified actuaries. The Company contributed $220 and $188 to its pension plans for the fiscal years ended September 30, 2023 and September 30, 2022. The Company anticipates that it will contribute at least the minimum required contribution of $279 to its pension plans in fiscal 2024. Benefit payments, which reflect future expected service as appropriate, are expected to be paid in each fiscal year as follows: (in thousands) 2024 $ 6,912 2025 7,103 2026 7,263 2027 7,321 2028 7,349 2028 to 2032 36,909 Defined Contribution Retirement Plans — The Company also sponsors several defined contribution retirement plans - the 401(k) matching programs. Expense for the defined contribution plans is computed as a percentage of participants’ compensation and was $5,483, $4,615 and $3,400 for the fiscal years ended September 30, 2023, September 30, 2022 and September 30, 2021, respectively. Multi-Employer Plan — The Company has a liability of $4,336 as of September 30, 2023 and $4,685 as of September 30, 2022 representing the Company’s proportionate share of a multi-employer pension plan which was exited prior to fiscal 2017.

STOCK INCENTIVE PLAN

STOCK INCENTIVE PLAN	12 Months Ended
STOCK INCENTIVE PLAN	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
STOCK INCENTIVE PLAN	5. STOCK INCENTIVE PLAN On November 21, 2019, the Company's board of directors approved the Atkore International Group Inc. 2020 Omnibus Incentive Plan (the “2020 Omnibus Incentive Plan”), which was subsequently approved by the Company’s shareholders on January 30, 2020. The 2020 Omnibus Incentive Plan provides for stock purchases and grants of other equity awards, including non-qualified stock options, stock purchase rights, restricted stock, restricted stock units (“RSUs”), performance shares, performance stock units (“PSUs”), stock appreciation rights, dividend equivalents and other stock-based awards to directors, officers, other employees and consultants. The 2020 Omnibus Incentive Plan replaces and succeeds the Atkore International Group Inc. 2016 Omnibus Incentive Plan (the “2016 Omnibus Incentive Plan”). The Company no longer grants awards from the 2016 Omnibus Incentive Plan. Awards previously granted under the 2016 Omnibus Incentive Plan were unaffected by the termination. A maximum of 1.8 million shares of common stock is reserved for issuance under the 2020 Omnibus Incentive Plan. All stock option awards have a ten year life. All share-based awards are expected to be fulfilled with new shares of common stock. Stock compensation expense is included in selling, general and administrative in the Company's consolidated statements of operations and was $21,101, $17,245 and $17,047 for fiscal years 2023, 2022 and 2021, respectively. The total income tax benefit recognized for share-based compensation arrangements was $2,706, $1,634 and $2,073 for fiscal years 2023, 2022 and 2021, respectively. Stock Options In accordance with ASC 718 Compensation - Stock Compensation, stock compensation expense for stock options is recorded on a straight-line basis over the requisite service period (generally the vesting period), net of actual forfeitures based on the grant-date fair value of the option under the equity accounting method. The assumptions used in the Black-Scholes option pricing model to value the options granted were as follows: Fiscal Year Ended September 30, 2023 September 30, 2022 September 30, 2021 Expected dividend yield — % — % — % Expected volatility 51 % 49 % 59 % Range of risk-free interest rates 3.92 % 1.40 % 0.52% Range of expected option lives 6 years 6 years 6 years Dividends are not paid on the Company’s common stock for fiscal 2023 and prior years. For grants during fiscal years ended 2023, 2022 and 2021, the expected volatility is based on the Company’s stock price volatility. The risk-free interest rate is based on the United States Treasury yield curve in effect at the time of the grant for periods corresponding with the expected life of the options. The expected life of options is estimated using the simplified method due to limited historical exercise activity. The Company does not estimate forfeitures, which are accounted for as they occur. Stock option activity for the period September 30, 2020 to September 30, 2023 was as follows: Shares Weighted-Average Exercise Price Weighted-Average Grant Date Fair Value Aggregate Intrinsic Value Weighted-Average Remaining Contractual Term (in years) Outstanding as of September 30, 2020 1,375 $ 15.66 $ 11,443 Granted 72 $ 29.80 Exercised (678) $ 12.30 $ 33,075 Forfeited — — Outstanding as of September 30, 2021 769 $ 19.95 $ 10.89 $ 51,441 Granted 42 $ 105.94 $ 49.39 Exercised (98) $ 12.58 $ 9.84 $ 8,703 Forfeited — — Outstanding as of September 30, 2022 713 $ 26.00 $ 13.29 $ 38,062 5.22 Granted 51 $ 101.66 $ 54.06 Exercised (74) $ 13.26 $ 9.56 $ 9,201 Forfeited — — Outstanding as of September 30, 2023 690 $ 32.93 $ 16.69 $ 80,152 9.75 Exercisable as of September 30, 2023 539 $ 23.45 $ 67,835 4.13 As of September 30, 2023, there was $1,117 of total unrecognized compensation expense related to non-vested options granted expected to be recognized over a weighted-average period of approximately 9.8 years. The total fair value of shares vested during fiscal years 2023, 2022 and 2021 was $1,924, $1,447 and $1,465, respectively. Cash received from stock option exercises for the fiscal years 2023, 2022 and 2021 was $973, $1,230 and $8,535, respectively. The actual tax benefit for the tax deductions from stock option exercises totaled $2,300, $2,176 and $8,228, respectively, for fiscal years 2023, 2022 and 2021. The Company does not settle any option exercises, under its current stock incentive plan, in cash. Restricted Stock Units Generally, RSUs granted under the 2020 Omnibus Incentive Plan vest ratably over three years. The fair value of RSU grants was based on the closing price of the Company's common stock on the date of grant. RSU compensation expense is recorded on a straight-line basis over the remaining vesting period. Changes to the Company’s nonvested RSU awards for the year ended September 30, 2023 were as follows: Shares Weighted-average grant-date fair value Nonvested as of September 30, 2020 405 $ 26.44 Granted 218 32.01 Vested (229) 23.78 Forfeited (10) 28.48 Nonvested as of September 30, 2021 384 30.30 Granted 100 103.94 Vested (208) 27.40 Forfeited (14) 49.23 Nonvested as of September 30, 2022 262 58.72 Granted 138 102.71 Vested (144) 47.43 Forfeited (10) 84.89 Nonvested as of September 30, 2023 246 $ 86.16 As of September 30, 2023, there was $10,782 of total unrecognized compensation expense related to non-vested RSUs granted, expected to be recognized over a weighted-average period of approximately 1.37 years. The total fair value of RSUs vested during fiscal years 2023, 2022 and 2021 was $17,878, $20,342 and $8,897 respectively. Performance Share Units The Company awards PSUs whose vesting is contingent upon meeting or exceeding certain market and performance conditions. The performance condition, which was based on an adjusted net income, represented 70% of the award and the market condition, which was based on Total Shareholder Return (“TSR”) of the Company's common stock relative to a peer group represented the remaining 30%. All PSUs cliff vest at the end of three years based on the satisfaction of the performance conditions. Expense for the performance condition based award is recorded when the achievement of the performance condition is considered probable of achievement and is recorded on a straight-line basis over the requisite service period. If such performance criteria are not met, no compensation cost is recognized and any recognized compensation cost is reversed. Expense for the market condition based award is recorded on a straight-line basis over the explicit service period. The grant-date fair value for the performance condition based awards represents the closing stock price on the date of grant. For the grants in fiscal 2023, 2022 and 2021, the closing stock price on the date of grant was $101.66, $105.94 and $29.80 respectively. The grant-date fair value for the market condition based awards was determined using the Monte-Carlo method. The assumptions used in the Monte-Carlo method to value the performance share awards granted during the fiscal year ended September 30, 2023 were as follows: September 30, 2023 September 30, 2022 September 30, 2021 Expected dividend yield — % — % — % Expected volatility 68 % 63 % 61% - Risk free interest rates 4.15 % 0.83 % 0.21 % Expected life 3 years 3 years 3 years Fair value $121.52 $122.25 $33.80 For the fiscal years ended 2023, 2022 and 2021, dividends are not paid on the Company’s common stock. For grants during fiscal year ended 2023, 2022 and 2021, the expected volatility is based on the Company’s stock price volatility. The risk-free interest rate is based on the United States Treasury yield curve in effect at the time of the grant for periods corresponding with the expected life of the award. The expected life of the award represents the weighted-average period of time that awards granted are expected to be outstanding, giving consideration to vesting schedules and expected exercise patterns. The Company does not estimate forfeitures, which are accounted for as they occur. Changes to the Company’s non-vested PSU awards for the year ended September 30, 2023 were as follows: Shares Weighted-average grant-date fair value Nonvested as of September 30, 2020 425 $ 25.15 Granted 156 31.67 Vested (171) 21.55 Adjustment for achieved performance upon issuance 57 22.95 Forfeited (14) 29.43 Nonvested as of September 30, 2021 453 $ 28.07 Granted 52 113.51 Vested (381) 18.17 Adjustment for achieved performance upon issuance 190 18.17 Forfeited (1) 57.61 Nonvested as of September 30, 2022 313 $ 48.19 Granted 69 110.71 Vested (190) 39.94 Adjustment for achieved performance upon issuance 83 39.31 Forfeited (1) 31.67 Nonvested as of September 30, 2023 273 $ 67.02

OTHER (INCOME) AND EXPENSE, NET

OTHER (INCOME) AND EXPENSE, NET	12 Months Ended
OTHER (INCOME) AND EXPENSE, NET	Sep. 30, 2023
Other Income, Nonoperating [Abstract]
OTHER (INCOME) AND EXPENSE, NET	6. OTHER (INCOME) AND EXPENSE, NET Other (income) and expense, net consisted of the following: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Gain on purchase of business $ — $ — $ (731) Undesignated foreign currency derivative instruments — (4,379) 2,201 Business interruption insurance recovery — — (15,500) Foreign exchange loss (gain) on intercompany loans (88) 5,342 (1,534) Pension-related expense (benefit) 579 (1,803) (2,368) Loss on assets held for sale 7,477 — — Other 1 350 (220) Other (income) and expense, net $ 7,969 $ (490) $ (18,152)

INCOME TAXES

INCOME TAXES	12 Months Ended
INCOME TAXES	Sep. 30, 2023
Income Tax Disclosure [Abstract]
INCOME TAXES	7. INCOME TAXES On August 16, 2022, the Inflation Reduction Act of 2022 (“IRA”) was enacted into law. The IRA contains significant tax law changes, including a corporate alternative minimum tax of 15% on adjusted financial statement income, which if applicable for the Company would be effective beginning October 1, 2023, a 1% excise tax on stock repurchases after December 31, 2022, and various tax incentives which include, but are not limited to, credits related to the manufacturing and selling of components used in the solar energy industry which took effect on January 1, 2023. The Company has recognized the benefit of credits related to the manufacturing and selling of components used in the solar energy industry in the income tax provision. Significant components of income before income taxes and income tax expense for the fiscal years ended September 30, 2023, September 30, 2022 and September 30, 2021 consisted of the following: (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Components of income before income taxes: United States $ 817,853 $ 1,174,109 $ 770,350 Non-U.S 32,437 29,511 9,651 Income before income taxes $ 850,290 $ 1,203,620 $ 780,001 Income tax expense: Current: United States: Federal $ 110,714 $ 228,141 $ 182,105 State 25,556 49,793 46,913 Non-U.S: 11,261 9,198 6,432 Current income tax expense $ 147,531 $ 287,132 $ 235,450 Deferred: United States: Federal $ 12,670 $ 3,174 $ (35,442) State 1,274 753 (7,281) Non-U.S: (1,085) (873) (583) Deferred income (benefit) tax expense 12,860 3,054 (43,306) Income tax expense $ 160,391 $ 290,186 $ 192,144 Differences between the statutory federal income tax rate and effective income tax rate are summarized below: (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Statutory federal tax 21 % 21 % 21 % Adjustments to reconcile to the effective income tax rate: State income taxes 3 % 3 % 4 % Stock-based compensation (1) % (1) % (1) % Solar tax credits (5) % — % — % Other 1 % 1 % 1 % Effective income tax rate 19 % 24 % 25 % The Company’s effective tax rate for fiscal 2023 differs from the statutory rate primarily due to state income taxes of $21,630 and solar tax credits of $39,493. The Company’s effective tax rate for fiscal 2022 differs from the statutory rate primarily due to state income taxes of $39,759, and limitations on executive compensation of $6,996 partially offset by $11,438 of excess tax benefit from share-based compensation. The Company’s effective tax rate for fiscal 2021 differs from the statutory rate primarily due to state income taxes of $30,680, current year valuation allowance expense of $2,190 and limitations on executive compensation of $2,587, partially offset by $7,352 of excess tax benefit from share-based compensation. Deferred income taxes result from temporary differences between the amount of assets and liabilities recognized for financial reporting and tax purposes. The components of the net deferred income tax assets are as follows: (in thousands) September 30, 2023 September 30, 2022 Deferred tax assets: Accrued liabilities and reserves $ 42,824 $ 47,582 Tax loss and credit carryforwards 20,648 17,272 Postretirement benefits — 583 Inventory 21,256 29,501 Lease obligations 29,722 17,779 Other 4,686 1,079 $ 119,136 $ 113,796 Deferred tax liabilities: Property, plant and equipment $ (37,814) $ (28,475) Intangible assets (49,084) (56,886) Right-of-use assets, net (29,583) (17,095) Other (5,376) (4,156) $ (121,857) $ (106,612) Net deferred tax liability before valuation allowance (2,721) 7,184 Valuation allowance (19,079) (13,415) Net deferred tax liability $ (21,800) $ (6,231) As of September 30, 2023, the Company has $7,744 of federal net operating loss carryforwards which do not expire and $23,599 of state net operating loss carryforwards which expire beginning in 2024 through 2036. In certain non-U.S. jurisdictions, the Company has net operating loss carryforwards of $68,189 which have an expiration period ranging from five years to unlimited. Valuation allowances have been established on net operating losses and other deferred tax assets in Luxembourg, Australia, France, China, and other foreign and United States state jurisdictions, as a result of the Company's determination that there is less than 50% likelihood that these assets will be realized. Evidence for this determination includes three year cumulative loss positions, future reversal of temporary differences, and expectations of future losses. As of September 30, 2023, and September 30, 2022, the Company had unrecognized tax benefits of $2,581 and $985 which, if recognized, would positively benefit the effective tax rate. The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense. As of September 30, 2023 and September 30, 2022, the Company had accrued interest and penalties of $236 and $77, respectively, in the consolidated balance sheets. A reconciliation of the beginning and ending amount of unrecognized tax benefit, excluding interest and penalties, is as follows: (in thousands) For the period from September 30, 2020 to September 30, 2023 Balance as of September 30, 2020 $ 1,614 Additions based on tax positions related to prior years 291 Additions based on tax positions related to current year 1,658 Settlements (230) Balance as of September 30, 2021 3,333 Additions based on tax positions related to prior years 322 Additions based on tax positions related to current year 342 Settlements (3,012) Balance as of September 30, 2022 985 Reductions based on tax positions related to prior years (75) Additions based on tax positions related to current year 1,792 Expiration of statute of limitations (121) Balance as of September 30, 2023 $ 2,581 During fiscal 2023, the balance of unrecognized tax benefits increased by $1,792 as a result of federal and various state jurisdictions’ uncertain positions, partially offset by a decrease of $196 as a result of completing tax audits and the expiration of the statute of limitations in various state jurisdictions. The related accrued penalties and interest for uncertain tax positions increased by $158. During fiscal 2022, the balance of unrecognized tax benefits decreased by $3,012 as a result of completing state tax audits and the expiration of the statute of limitations in various state jurisdictions, partially offset by an increase of $664, primarily related to various state jurisdictions’ uncertain tax positions. The related accrued penalties and interest for uncertain tax positions decreased by $183. During fiscal 2021, the balance of unrecognized tax benefits increased by $1,949 as a result of federal and various state jurisdictions' uncertain tax positions, partially offset by a decrease of $230 as a result of completing tax audits and the expiration of the statute of limitations in various state jurisdictions. The related accrued penalties and interest for uncertain tax positions increased by $72. Many of the Company’s uncertain tax positions relate to tax years that remain subject to audit by the taxing authorities. The following tax years remain subject to examination by the major tax jurisdictions as follows: Jurisdiction Years Open to Audit United States 2020, 2021 and 2022 The Company's income tax returns are examined periodically by various taxing authorities. The Company is currently under examination in various state jurisdictions. Based on the current status of its income tax audits, the Company believes that it is reasonably possible that there would be no material changes to the unrecognized tax benefits in the next twelve months. Other Income Tax Matters — Prior to the passage of the TCJA, foreign undistributed earnings were generally subject to U.S. taxation when repatriated. The TCJA imposed a one-time transition tax on previously untaxed accumulated earnings of foreign subsidiaries. The Company has accumulated earnings and profits deficit, therefore did not record an additional tax liability for the transition tax. The TCJA adopts a new quasi-territorial tax regime that eliminates U.S income taxes on dividends from foreign subsidiaries. The Company may still be liable for foreign taxes, such as withholding taxes, if earnings are repatriated. For the fiscal year ended September 30, 2023, the Company recorded a $98 provision for withholding taxes on the planned distribution of income from one of its European subsidiaries. The Company did not record income tax or non-income tax expense related to the remaining foreign earnings, and did not record any deferred tax liabilities for any basis differences in investments in subsidiaries as the earnings are expected to be indefinitely reinvested, the investments are essentially permanent in duration, or the Company has concluded that there will be no additional tax liability as a result of the distribution of the income. As of September 30, 2023, certain subsidiaries had approximately $131,056 of undistributed income that the Company intends to permanently reinvest. A liability could arise if the Company's intention to permanently reinvest such income were to change and amounts are distributed by such subsidiaries or if such subsidiaries are ultimately disposed of. It is not practicable to estimate the additional income taxes related to permanently reinvested income or the basis differences related to investments in subsidiaries.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
EARNINGS PER SHARE	Sep. 30, 2023
Earnings Per Share [Abstract]
EARNINGS PER SHARE	8. EARNINGS PER SHARE The Company calculates basic and diluted earnings per common share using the two-class method. Under the two-class method, net earnings are allocated to each class of common stock and participating securities as if all of the net earnings for the period had been distributed. The Company's participating securities consist of share-based payment awards that contain a non-forfeitable right to receive dividends and therefore are considered to participate in undistributed earnings with common stockholders. Basic earnings per common share excludes dilution and is calculated by dividing the net earnings allocable to common stock by the weighted-average number of common stock outstanding for the period. Diluted earnings per common share is calculated by dividing net earnings allocated to common stock by the weighted-average number of shares outstanding for the period, as adjusted for the potential dilutive effect of non-participating share-based awards. The following table sets forth the computation of basic and diluted earnings per share: Fiscal Year Ended (in thousands, except per share data) September 30, 2023 September 30, 2022 September 30, 2021 Numerator: Net income $ 689,899 $ 913,434 $ 587,857 Less: Undistributed earnings allocated to participating securities 10,637 14,460 11,380 Net income available to common shareholders $ 679,262 $ 898,974 $ 576,477 Denominator: Basic weighted average common shares outstanding 38,797 43,717 46,569 Effect of dilutive securities: Non-participating employee stock options (1) 531 563 737 Diluted weighted average common shares outstanding 39,328 44,280 47,306 Basic earnings per share $ 17.51 $ 20.56 $ 12.38 Diluted earnings per share $ 17.27 $ 20.30 $ 12.19 (1) There were no Stock options to shares of common stock were outstanding during the years ended September 30, 2023, September 30, 2022, and September 30, 2021, respectively, Any options available would not be included in the calculation of diluted earnings per share as the impact of these would have been anti-dilutive.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE LOSS	12 Months Ended
ACCUMULATED OTHER COMPREHENSIVE LOSS	Sep. 30, 2023
Equity [Abstract]
ACCUMULATED OTHER COMPREHENSIVE LOSS	9. ACCUMULATED OTHER COMPREHENSIVE LOSS The following table presents the changes in accumulated other comprehensive loss by component, net of tax: (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of September 30, 2021 $ (19,318) $ (9,408) $ (28,726) Other comprehensive (loss) income before reclassifications 2,051 (23,943) (21,892) Amounts reclassified from accumulated other comprehensive loss 472 — 472 Net current period other comprehensive (loss) income 2,523 (23,943) (21,420) Balance as of September 30, 2022 $ (16,795) $ (33,351) $ (50,146) Other comprehensive income (loss) before reclassifications 5,493 10,212 15,705 Amounts reclassified from accumulated other comprehensive loss 501 — 501 Net current period other comprehensive income (loss) 5,994 10,212 16,206 Balance as of September 30, 2023 $ (10,801) $ (23,139) $ (33,940) The following is a summary of the amounts reclassified from accumulated other comprehensive loss to net income: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Amortization of defined benefit pension items: Amortization of net loss (included within other income, net) $ 667 $ 631 $ 1,327 Tax expense (166) (159) (337) Net reclassifications for the period $ 501 $ 472 $ 990

INVENTORIES, NET

INVENTORIES, NET	12 Months Ended
INVENTORIES, NET	Sep. 30, 2023
Inventory Disclosure [Abstract]
INVENTORIES, NET	10. INVENTORIES, NET A majority of the Company records inventory at the lower of cost (primarily last in, first out, or “LIFO”) or market or net realizable value, as applicable. Approximately 82% and 82% of the Company's inventories are valued at the lower of LIFO cost or market at September 30, 2023 and September 30, 2022, respectively. (in thousands) September 30, 2023 September 30, 2022 Purchased materials and manufactured parts, net $ 231,518 $ 166,038 Work in process, net 60,524 61,182 Finished goods, net 201,810 227,291 Inventories, net $ 493,852 $ 454,511 Total inventories would be $29,826 higher and $64,550 higher than reported as of September 30, 2023 and September 30, 2022, respectively, if the first-in, first-out method was used for all inventories. During the years ended September 30, 2023 and September 30, 2022, inventory quantities in specific pools were lower at the end of the period than the quantities at the beginning of the period. This reduction resulted in a liquidation of LIFO inventory quantities carried at net lower costs prevailing in the respective prior years as compared with the cost of respective current year purchases. The effect of this inventory reduction resulted in decreased cost of goods sold and increased operating income of approximately $2,394 and $248.

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT	12 Months Ended
PROPERTY, PLANT AND EQUIPMENT	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	11. PROPERTY, PLANT AND EQUIPMENT As of September 30, 2023 and September 30, 2022, property, plant and equipment at cost and accumulated depreciation were as follows: (in thousands) September 30, 2023 September 30, 2022 Land $ 29,082 $ 22,113 Buildings and related improvements 182,760 172,633 Machinery and equipment 513,563 427,460 Leasehold improvements 15,910 10,512 Software 47,072 36,884 Construction in progress 206,311 99,491 Property, plant and equipment, at cost 994,698 769,093 Accumulated depreciation (435,657) (378,873) Property, plant and equipment, net $ 559,041 $ 390,220

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	12 Months Ended
GOODWILL AND INTANGIBLE ASSETS	Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	12. GOODWILL AND INTANGIBLE ASSETS Goodwill — C hanges in the carrying amount of goodwill are as follows: Segment (in thousands) Electrical Safety & Infrastructure Total Balance as of September 30, 2021 $ 155,471 $ 43,577 $ 199,048 Goodwill acquired during year 87,964 9,431 97,395 Exchange rate effects (6,727) (386) (7,113) Balance as of September 30, 2022 $ 236,708 $ 52,622 $ 289,330 Goodwill acquired during year 18,669 14 18,683 Impairment (1,721) — (1,721) Other purchase accounting adjustments 1,989 — 1,989 Exchange rate effects 2,782 43 2,825 Balance as of September 30, 2023 $ 258,427 $ 52,679 $ 311,106 Goodwill balances include $5,645 and $43,000 of accumulated impairment losses within the Electrical and Safety & Infrastructure segments, respectively, as of September 30, 2023 and September 30, 2022. As described in Note 6, “Other (Income) and Expense, net”, the Company is finalizing plans to exit operations in Russia and expects to sell the related business at a loss. The Company recognized an impairment of $7,477 for the year ended September 30, 2023, which includes $1,721 of impaired goodwill that was allocated from the reporting unit on a relative fair value basis. Intangible Assets — The following table provides the gross carrying value, accumulated amortization, and net carrying value for each major class of intangible assets: September 30, 2023 September 30, 2022 (in thousands) Weighted Average Useful Life (Years) Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Amortizable Intangible Assets: Customer relationships 11 $ 596,396 $ (318,058) $ 278,338 $ 532,768 $ (267,940) $ 264,828 Other 8 43,633 (20,406) 23,227 35,681 (10,602) 25,079 Total 640,029 (338,464) 301,565 568,449 (278,542) 289,907 Indefinite-lived Intangible Assets: Trade names 92,806 — 92,806 92,799 — 92,799 Total $ 732,835 $ (338,464) $ 394,372 $ 661,248 $ (278,542) $ 382,706 Amortization expense for the fiscal years ended September 30, 2023, September 30, 2022 and September 30, 2021 was $57,804, $36,176 and $33,644, respectively. Expected amortization expense for intangible assets over the next five years and thereafter is as follows (in thousands): 2024 $ 54,421 2025 43,341 2026 40,741 2027 39,621 2028 29,432 2029 and thereafter 94,009

DEBT

DEBT	12 Months Ended
DEBT	Sep. 30, 2023
Debt Disclosure [Abstract]
DEBT	13. DEBT Debt as of September 30, 2023 and September 30, 2022 was as follows: (in thousands) September 30, 2023 September 30, 2022 New Senior Secured Term Loan Facility due May 26, 2028 $ 371,667 $ 371,381 Senior Notes Due June 1, 2031 400,000 400,000 ABL Credit Facility — — Deferred financing costs (8,980) (10,844) Long-term debt $ 762,687 $ 760,537 During fiscal 2021, the Company made voluntary prepayments of principal on the New Senior Secured Term Loan Facility of $26,000. The voluntary prepayment on the New Senior Secured Term Loan Facility resulted in the removal of all principal payment requirements until the contractual maturity of the debt in fiscal 2028. No additional payments were made in fiscal 2022 or fiscal 2023. As of September 30, 2023, future contractual maturities of long-term debt are as follows (in thousands): 2024 $ — 2025 — 2026 — 2027 — 2028 373,000 2029 and thereafter 400,000 Total $ 773,000 Senior Notes - On May 26, 2021, the Company completed the issuance and sale of the $400 million aggregate principal amount of 4.25% Senior Notes due 2031 (the “Senior Notes”) in a private offering. The Senior Notes were sold only to qualified institutional buyers in compliance with Rule 144A of the Securities Act of 1933, as amended (the “Securities Act”), and to non-U.S. persons outside of the United States in compliance with Regulation S of the Securities Act. New Senior Secured Term Loan Facility - On May 26, 2021, the Company entered into a new $400 million senior secured term loan facility (the “New Senior Secured Term Loan Facility”). The New Senior Secured Term Loan Facility will mature on May 26, 2028 and borrowings thereunder bear interest at the rate of either (x) LIBOR (with a floor of 0.50%) plus 2.00%, or (y) an alternate base rate (with a floor of 1.50%) plus 1.00%. The New Senior Secured Term Loan Facility has an annual amortization rate of 1.00%. On March 15, 2023, the Company entered into an amendment to the New Senior Secured Term Loan Facility to implement a forward-looking interest rate based on the Secured Overnight Financing Rate (“SOFR”) in lieu of LIBOR, consisting of an applicable margin of 2.00% and a credit spread adjustment of (i) 0.11448% for a one-month interest period, (ii) 0.26161% for a three-month interest period and (iii) 0.42826% for a six-month interest period. ABL Credit Facility — On August 28 2020, AII amended the ABL Credit Facility (the “Amended ABL Facility”). The amendment, among other things, extended the maturity of the facility to August 28, 2023, and increased the interest rate margins applicable to loans under the facility to (i) in the case of United States dollar-denominated loans, either (x) LIBOR plus an applicable margin ranging from 1.75% to 2.25%, or (y) an alternate base rate plus an applicable margin ranging from 0.75% to 1.25%, each based on available loan commitments or (ii) in the case of Canadian dollar-denominated loans, either (x) the BA rate plus an applicable margin ranging from 1.75% to 2.25% or (y) a Canadian prime rate plus an applicable margin ranging from 0.75% to 1.25%, each based on available loan commitments. The Amended ABL Credit Facility bears a commitment fee, payable quarterly in arrears, of 0.375% per annum. The Amended ABL Credit Facility also bears customary letter of credit fees. The revisions to the ABL Credit Facility were accounted for as a debt extinguishment, resulting in immediate expensing of unamortized financing costs of $273 for the year ended September 30, 2020. On May 26, 2021, the Company entered into an amendment to the ABL Credit Facility. The amendment (i) extends the maturity of the facility to the earlier of five years from entering into the amendment or 91 days prior to the maturity date of the New Senior Secured Term Loan Facility if at least $100 million of obligations remain outstanding under the New Senior Secured Term Loan Facility on such date (ii) decreases the interest rate margins applicable to loans under the facility to (a) in the case of United States dollar-denominated loans, either (x) LIBOR plus an applicable margin ranging from 1.25% to 1.75%, or (y) an alternate base rate plus an applicable margin ranging from 0.25% to 0.75% or (b) in the case of Canadian dollar-denominated loans, either (x) the bankers acceptance rate plus an applicable margin ranging from 1.25% to 1.75% or (y) a Canadian prime rate plus an applicable margin ranging from 0.25% to 0.75%. (iii) decreases the fee payable with respect to unutilized availability under the facility from 0.375% to 0.30%, depending on the remaining availability under the ABL Credit Facility the rate may decrease to 0.25% and (iv) made certain other changes agreed with the lenders under the ABL Credit Facility. Further, on March 24, 2023, the Company entered into an amendment to the Amended ABL Credit Facility to implement a forward-looking interest rate based on SOFR in lieu of LIBOR, consisting of an applicable margin ranging from 1.25% to 1.75% and a credit spread adjustment of 0.10%. The Amended ABL Credit Facility has aggregate commitments of $325,000 and is guaranteed by AII, the United States subsidiaries owned directly or indirectly by AII and certain other restricted subsidiaries of AII that AII causes to be a subsidiary guarantor from time to time including as of the closing date for the Amended ABL Credit Facility, Columbia-MBF, Inc., a corporation formed by amalgamation under the laws of Canada (“Columbia-MBF”). AII's availability under the ABL Credit Facility was $322,406 and $312,095 as of September 30, 2023 and September 30, 2022, respectively. Availability under the ABL Credit Facility is subject to a borrowing base equal to the sum of 85% of eligible accounts receivable plus the lesser of (i) 80% of eligible inventory of each borrower and guarantor, valued at the lower of cost and fair market value and (ii) 85% of the net orderly liquidation value of eligible inventory, subject to certain limitations. There were no borrowings outstanding under the ABL Credit Facility as of September 30, 2023 and September 30, 2022, respectively. The New Senior Secured Term Loan Facility and the ABL Credit Facility are secured by all of the assets of AII and the guarantors under such facilities. The New Senior Secured Term Loan Facility has priority over all real property, plant and equipment, intellectual property and capital stock of AII and any guarantor and any documents or instruments evidencing the foregoing assets. The ABL Credit Facility has second priority over the foregoing assets. The ABL Credit Facility has first priority over cash and cash equivalents, accounts receivable, inventory and other documents and instruments evidencing the foregoing assets. The New Senior Secured Term Loan Facility has second priority over the foregoing assets. The aforementioned debt instruments contain customary covenants typical for this type of financing, including limitations on indebtedness, restricted payments including dividends, liens, restrictions on distributions from restricted subsidiaries, sales of assets, affiliate transactions and mergers and consolidations. Many of these covenants are only applicable when the Company has surpassed certain thresholds relating to its indebtedness and availability under the ABL Credit Facility. Additionally, these debt instruments include customary events of default, including, among other things, payment default, covenant default, payment defaults and accelerations under other indebtedness, judgment defaults and bankruptcy, insolvency or reorganization affecting the Company or certain of its subsidiaries. Use of Proceeds - In fiscal 2021, the proceeds from the Senior Notes and the New Senior Secured Term Loan Facility were used to repay the remaining principal of the existing First Lien Term Loan Facility of $772.0 million and $4.0 million of accrued interest. The Company accounted for the repayment of the First Lien Term Loan Facility as an extinguishment of debt and recorded a $4.2 million loss on extinguishment of debt. The Company accounted for the amendment to the ABL Credit Facility as a modification of debt. The ABL Credit Facility has remained unused in both fiscal 2022 and fiscal 2023.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
FAIR VALUE MEASUREMENTS	Sep. 30, 2023
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	14. FAIR VALUE MEASUREMENTS Certain assets and liabilities are required to be recorded at fair value on a recurring basis. The Company periodically uses forward currency contracts to hedge the effects of foreign exchange relating to intercompany balances denominated in a foreign currency. These derivative instruments are not formally designated as hedges by the Company. Short-term forward currency contracts are recorded in prepaid expenses and other current assets or other current liabilities and long-term forward currency contracts are recorded in other long-term assets or other long-term liabilities in the consolidated balance sheets for the applicable period. The fair value gains and losses are included in other income, net within the consolidated statements of operations. See Note 6, “Other (Income) and Expense, net” for further detail. The Company had no active forward currency contracts or other derivative instruments as of September 30, 2023, or September 30, 2022, with the last such contract having expired in the third quarter of fiscal 2022. The Company had £37.4 million of undesignated forward currency contracts as of September 30, 2021. Cash flows associated with derivative financial instruments are recognized in the operating section of the consolidated statements of cash flows. The fair value of forward currency contracts is calculated by reference to current forward exchange rates for contracts with similar maturity profiles. The following table presents the recurring assets and liabilities measured at fair value as of September 30, 2023 and September 30, 2022 in accordance with the fair value hierarchy: September 30, 2023 September 30, 2022 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Cash equivalents $ 321,282 $ — $ — $ 291,757 $ — $ — Forward currency contracts — — — — — — Liabilities Forward currency contracts — $ — — — $ — — The Company’s remaining financial instruments consist primarily of cash, accounts receivable and accounts payable whose carrying value approximate their fair value due to their short-term nature. The estimated fair value of financial instruments not carried at fair value in the consolidated balance sheets were as follows: September 30, 2023 September 30, 2022 (in thousands) Carrying Value Fair Value Carrying Value Fair Value New Senior Secured Term Loan Facility due May 26, 2028 $ 373,000 $ 372,068 $ 373,000 $ 370,203 Senior Notes due June 2031 400,000 334,368 400,000 318,912 Total debt $ 773,000 $ 706,436 $ 773,000 $ 689,115 In determining the approximate fair value of its long-term debt, the Company used the trading value among financial institutions, which were classified within Level 2 of the fair value hierarchy. The carrying value of the ABL Credit Facility approximates fair value due to it being market-linked variable rate debt.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	15. COMMITMENTS AND CONTINGENCIES The Company has obligations related to commitments to purchase certain goods. As of September 30, 2023, such obligations were $127,756 for fiscal 2024, $3,816 for fiscal 2025 and $4,800 thereafter. These amounts represent open purchase orders for materials used in production. Insurable Liabilities — The Company maintains policies with various insurance companies for its workers’ compensation, product, property, general, auto, and executive liability risks. The insurance policies that the Company maintains have various retention levels and excess coverage limits. The establishment and update of liabilities for unpaid claims, including claims incurred but not reported, is based on management's estimate as a result of the assessment by the Company's claim administrator of each claim and an independent actuarial valuation of the nature and severity of total claims. The Company utilizes a third-party claims administrator to pay claims, track and evaluate actual claims experience, and ensure consistency in the data used in the actuarial valuation. Legal Contingencies — Historically, a number of lawsuits have been filed against the Company and the Company has also received other claim demand letters alleging that the Company's anti-microbial coated steel sprinkler pipe, which the Company has not manufactured or sold for several years, is incompatible with chlorinated polyvinyl chloride and caused stress cracking in such pipe manufactured by third parties when installed together in the same sprinkler system, which the Company refers to collectively as the “Special Products Claims.” Tyco International Ltd. (“Tyco”), now Johnson Controls, Inc. (“JCI”), has a contractual obligation to indemnify the Company in respect of all remaining and future claims of incompatibility between the Company's antimicrobial coated steel sprinkler pipe and CPVC pipe used in the same sprinkler system. When Special Products Claims arise, JCI has defended and indemnified the Company as required. As of September 30, 2023, the Company believes that the range of reasonably possible losses for Special Products Claims and other product liabilities is between $1,000 and $8,000. At this time, the Company does not expect the outcome of the Special Products Claims proceedings, either individually or in the aggregate, to have a material adverse effect on its business, financial condition, results of operations or cash flows, and the Company believes that its reserves are adequate for all remaining contingencies for Special Products Claims. During the year ended September 30, 2020, one of the Company’s manufacturing facilities experienced a flood which resulted in damages to certain property, plant and equipment. This facility was covered under the Company’s property and casualty loss and business interruption insurance policies. During the year ended September 30, 2021, the Company settled the related insurance claim and received $15,500 of business interruption recovery proceeds related to this incident. The amount was recorded as other income within the consolidated statements of operations for the year ended September 30, 2021. In addition to the matters discussed above, from time to time, the Company is subject to a number of disputes, administrative proceedings and other claims arising out of the ordinary conduct of the Company's business. These matters generally relate to disputes arising out of the use or installation of the Company’s products, product liability litigation, contract disputes, patent infringement accusations, employment matters, personal injury claims and similar matters. On the basis of information currently available to the Company, it does not believe that existing proceedings and claims will have a material adverse effect on its business, financial condition, results of operations or cash flows. However, litigation is unpredictable, and the Company could incur judgments or enter into settlements for current or future claims that could adversely affect its business, financial condition, results of operations or cash flows.

GUARANTEES

GUARANTEES	12 Months Ended
GUARANTEES	Sep. 30, 2023
Guarantees and Product Warranties [Abstract]
GUARANTEES	16. GUARANTEES The Company has outstanding letters of credit totaling $2,594 supporting workers’ compensation and general liability insurance policies and surety bonds primarily related to performance guarantees on supply agreements and construction contracts, and payment of duties and taxes totaling $37,087 as of September 30, 2023. In disposing of assets or businesses, the Company often provides representations, warranties and indemnities to cover various risks including unknown damage to the assets, environmental risks involved in the sale of real estate, liability to investigate and remediate environmental contamination at waste disposal sites and manufacturing facilities, and unidentified tax liabilities and legal fees related to periods prior to disposition. The Company does not have the ability to estimate the potential liability from such indemnities because they relate to unknown conditions. However, the Company has no reason to believe that these uncertainties would have a material adverse effect on the Company's business, financial condition, results of operations or cash flows. In the normal course of business, the Company is liable for product performance and contract completion. In the opinion of management, such obligations will not have a material adverse effect on the Company's business, financial condition, results of operations or cash flows.

SEGMENT INFORMATION

SEGMENT INFORMATION	12 Months Ended
SEGMENT INFORMATION	Sep. 30, 2023
Segment Reporting [Abstract]
SEGMENT INFORMATION	17. SEGMENT INFORMATION The Electrical segment manufactures high quality products used in the construction of electrical power systems including conduit, cable, and installation accessories. This segment serves contractors in partnership with the electrical wholesale channel. The Safety & Infrastructure segment designs and manufactures solutions including metal framing, mechanical pipe, perimeter security, and cable management for the protection and reliability of critical infrastructure. These solutions are marketed to contractors, original equipment manufacturers and end users. Both segments use Adjusted EBITDA as the primary measure of profit and loss. Segment Adjusted EBITDA is the income (loss) before income taxes, adjusted to exclude unallocated expenses, depreciation and amortization, interest expense, net, loss on extinguishment of debt, restructuring charges, impairment charges, stock-based compensation, certain legal matters, transaction costs, gain on purchase of business, gain on sale of a business and other items, such as inventory reserves and adjustments, loss on disposal of property, plant and equipment, insurance recovery related to damages of property, plant and equipment, release of indemnified uncertain tax positions, and realized or unrealized gain (loss) on foreign currency impacts of intercompany loans and related forward currency derivatives. Intersegment transactions primarily consist of product sales at designated transfer prices on an arm's-length basis. Gross profit earned and reported within the segment is eliminated in the Company’s consolidated results. Certain manufacturing and distribution expenses are allocated between the segments on a pro rata basis due to the shared nature of activities. Recorded amounts represent a proportional amount of the quantity of product produced for each segment. Certain assets, such as machinery and equipment and facilities, are not allocated to each segment despite serving both segments. These shared assets are reported within the Safety & Infrastructure segment. We allocate certain corporate operating expenses that directly benefit our operating segments, such as insurance and information technology, on a basis that reasonably approximates an estimate of the use of these services. Fiscal year ended September 30, 2023 September 30, 2022 September 30, 2021 (in thousands) External Net Sales Inter- segment Sales Adjusted EBITDA External Net Sales Inter- segment Sales Adjusted EBITDA External Net Sales Inter- segment Sales Adjusted EBITDA Electrical $ 2,675,050 $ 25 $ 1,004,853 $ 3,013,755 $ — $ 1,273,410 $ 2,229,862 $ 3,437 $ 873,868 Safety & Infrastructure 843,711 447 $ 103,231 900,194 394 $ 138,390 698,152 168 $ 81,827 Eliminations — (471) (394) — (3,605) Consolidated operations $ 3,518,761 $ — $ 3,913,949 $ — $ 2,928,014 $ — Capital Expenditures Total Assets (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 September 30, 2023 September 30, 2022 September 30, 2021 Electrical $ 137,485 $ 61,721 $ 34,995 $ 1,715,419 $ 1,524,670 $ 1,122,835 Safety & Infrastructure 69,475 38,280 22,407 753,821 618,331 482,942 Unallocated 11,928 35,775 7,072 465,769 455,995 604,322 Consolidated operations $ 218,888 $ 135,776 $ 64,474 $ 2,935,009 $ 2,598,996 $ 2,210,099 Presented below is a reconciliation of operating segment Adjusted EBITDA to Income before income taxes: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Operating segment Adjusted EBITDA Electrical $ 1,004,853 $ 1,273,410 $ 873,868 Safety & Infrastructure 103,231 138,390 81,827 Total $ 1,108,083 $ 1,411,800 $ 955,695 Unallocated expenses (a) (65,956) (70,010) (58,148) Depreciation and amortization (115,524) (84,415) (78,557) Interest expense, net (35,232) (30,676) (32,899) Loss on extinguishment of debt — — (4,202) Stock-based compensation (21,101) (17,245) (17,047) Transaction costs (968) (3,424) (667) Loss on assets held for sale (7,477) — — Other (b) (11,535) (2,410) 15,826 Income before income taxes $ 850,290 $ 1,203,620 $ 780,001 (a) Represents unallocated selling, general and administrative activities and associated expenses including, in part, executive, legal, finance, human resources, information technology, business development and communications, as well as certain costs and earnings of employee-related benefits plans, such as stock-based compensation and a portion of self-insured medical costs. (b) Represents other items, such as inventory reserves and adjustments, loss on disposal of property, plant and equipment, insurance recovery related to damages of property, plant and equipment, release of indemnified uncertain tax positions and realized or unrealized gain (loss) on foreign currency impacts of intercompany loans, restructuring charges, gain on purchase of business, impairment charges, and related forward currency derivatives. The Company’s long-lived assets and net sales by geography were as follows: Long-lived assets Net sales (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 September 30, 2023 September 30, 2022 September 30, 2021 United States $ 612,066 $ 410,263 $ 258,069 $ 3,150,143 $ 3,552,893 $ 2,637,118 Other Americas 8,655 7,195 6,180 94,064 102,626 53,151 Europe 52,498 38,396 45,917 228,885 213,581 183,985 Asia-Pacific 6,569 5,400 6,569 45,669 44,849 53,760 Total $ 679,788 $ 461,255 $ 316,735 $ 3,518,761 $ 3,913,949 $ 2,928,014 The table below shows the amount of net sales from external customers for each of the Company’s product categories which accounted for 10% or more of consolidated net sales in any of the last three fiscal years: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Metal Electrical Conduit and Fittings $ 529,083 $ 635,481 $ 612,137 Plastic Pipe Conduit and Fittings 1,252,422 1,479,331 893,199 Electrical Cable and Flexible Conduit 506,994 535,194 424,411 Other Electrical products (a) 386,551 363,749 300,115 Electrical 2,675,050 3,013,755 2,229,862 Mechanical Tube 367,730 445,453 395,289 Other Safety & Infrastructure products (b) 475,982 454,741 302,863 Safety & Infrastructure 843,711 900,194 698,152 Net sales $ 3,518,761 $ 3,913,949 $ 2,928,014 (a) Other Electrical products includes International Cable Management, Fiberglass Conduit and Corrosion Resistant Conduit (b) Other S&I products includes Metal Framing and Fittings, Construction Services, Perimeter Security and Cable Management Risks and Concentrations Concentration of Credit Risk — The Company extends credit to various customers in the retail and construction industries. Collection of trade receivables may be affected by changes in economic or other industry conditions and may, accordingly, impact the Company's overall credit risk. Although the Company generally does not require collateral, the Company performs ongoing credit evaluations of customers and maintains reserves for potential credit losses. As of September 30, 2023, Sonepar USA represented 14% and CED National represented 11% of the Company’s accounts receivable, with no significant amounts past due. As of September 30, 2022, one customer, CED National represented 10% of the Company’s accounts receivable, with no significant amounts past due. For fiscal 2023, one customer, Sonepar USA accounted for more than 10% of sales, for fiscal 2022 and 2021, no single customer accounted for more than 10% of sales.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Sep. 30, 2023
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On November 17, 2023, the Company announced that the board of directors approved a quarterly dividend program under which the Company intends to pay quarterly cash dividends on its common stock.

SCHEDULE I - CONDENSED FINANCIA

SCHEDULE I - CONDENSED FINANCIAL INFORMATION	12 Months Ended
SCHEDULE I - CONDENSED FINANCIAL INFORMATION	Sep. 30, 2023
Condensed Financial Information Disclosure [Abstract]
SCHEDULE I - CONDENSED FINANCIAL INFORMATION	SCHEDULE I ATKORE INC. (PARENT) CONDENSED FINANCIAL INFORMATION CONDENSED BALANCE SHEETS (in thousands, except share and per share data) September 30, 2023 September 30, 2022 Assets Investment in subsidiary $ 1,468,119 $ 1,249,787 Total Assets $ 1,468,119 1,249,787 Liabilities and Equity Total Liabilities $ — $ — Equity: Common stock, $0.01 par value, 1,000,000,000 shares authorized, 37,317,893 and 41,351,350 shares issued and outstanding, respectively $ 374 $ 415 Treasury stock, held at cost, 0 and 260,900 shares, respectively — (2,580) Additional paid-in capital 506,783 500,117 Retained earnings 994,902 801,981 Accumulated other comprehensive loss (33,940) (50,146) Total Equity 1,468,119 1,249,787 Total Liabilities and Equity 1,468,119 $ 1,249,787 See Notes to Condensed Financial Information SCHEDULE I ATKORE INC. (PARENT) CONDENSED FINANCIAL INFORMATION CONDENSED STATEMENTS OF OPERATIONS Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Equity in net income of subsidiary $ 689,899 $ 913,434 $ 587,857 Net income 689,899 913,434 587,857 Other comprehensive (loss) income of subsidiary, net of tax 16,206 (21,420) 13,828 Comprehensive income $ 706,105 $ 892,014 $ 601,685 See Notes to Condensed Financial Information SCHEDULE I ATKORE INC. (PARENT) CONDENSED FINANCIAL INFORMATION CONDENSED STATEMENTS OF CASH FLOWS For the Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Cash Flows from Operating Activities: Net cash provided by operating activities $ — $ — $ — Cash Flows from Investing Activities: Distribution received from subsidiary 491,033 500,161 135,066 Distribution paid to subsidiary 14,428 24,045 (2,660) Net cash provided by investing activities 505,461 524,206 132,406 Cash Flows from Financing Activities: Issuance of common stock, net of taxes withheld (14,428) (24,045) 2,660 Repurchase of common shares (491,033) (500,161) (135,066) Net cash used in financing activities (505,461) (524,206) (132,406) Net change in cash and cash equivalents — — — Cash and cash equivalents: Beginning — — — Ending $ — $ — $ — See Notes to Condensed Financial Information SCHEDULE I ATKORE INC. (PARENT) CONDENSED FINANCIAL INFORMATION NOTES TO CONDENSED FINANCIAL INFORMATION (dollars in thousands) 1. Description of Atkore Inc. Atkore Inc. (the “Company,” “Parent” or “Atkore”) was incorporated in the State of Delaware on November 4, 2010 under the name Atkore International Group Inc. The Company was the stockholder of Atkore International Holdings Inc. (“AIH”), which was the sole stockholder of Atkore International Inc. (“AII”). On December 31, 2022, AIH merged into AII, with AII being the surviving entity. Accordingly, Atkore is now the sole stakeholder of AII. Prior to the transactions described below, all of the capital stock of AII was owned by Tyco International Ltd. (“Tyco”). The business of AII was operated as the Tyco Electrical and Metal Products (“TEMP”) business of Tyco. Atkore was initially formed by Tyco as a holding company to hold ownership of TEMP. On November 9, 2010, Tyco announced that it had entered into an agreement to sell a majority interest in TEMP to CD&R Allied Holdings, L.P. (the “CD&R Investor”), an affiliate of the private equity firm Clayton Dubilier & Rice, LLC (“CD&R”). On December 22, 2010, the transaction was completed and CD&R acquired shares of a newly created class of cumulative convertible preferred stock (the “Preferred Stock”) of the Company. The Preferred Stock initially represented 51% of the Company's outstanding capital stock (on an as-converted basis). On December 22, 2010, the Company also issued common stock (the “Common Stock”) to Tyco's wholly owned subsidiary, Tyco International Holding S.à.r.l. (“Tyco Seller”), that initially represented the remaining 49% of the Company's outstanding capital stock. Subsequent to December 22, 2010, the Company has operated as an independent, stand-alone entity. On March 6, 2014, the Company entered into a non-binding letter of intent (the “Letter of Intent”) with Tyco for the acquisition (the “Acquisition”) of 40.3 million shares of Common Stock held by Tyco Seller. On April 9, 2014, the Company paid $250,000 to Tyco Seller to redeem the shares, which were subsequently retired. The Company paid $2,000 of expenses related to the share redemption. In a separate transaction on the same date, the CD&R Investor converted its Preferred Stock and accumulated Preferred Dividends into Common Stock. As a result, Common Stock is the Company's sole issued and outstanding class of securities. The Parent has no significant operations or assets other than its indirect ownership of the equity of AII. Accordingly, the Parent is dependent upon distributions from AII to fund its obligations. However, under the terms of the agreements governing AII's borrowings, AII's ability to pay dividends or lend to Atkore Holding or the Parent, is restricted. While certain exceptions to the paying dividends or lending funds restrictions exist, these restrictions have resulted in the restricted net assets (as defined in Rule 4-08(e)(3) of Regulation S-X) of the Company's subsidiaries exceeding 25% of the consolidated net assets of the Company and its subsidiaries. Atkore Holding has no obligations to pay dividends to the Parent except to pay specified amounts to Parent in order to fund the payment of the Parent's tax obligations. 2. Basis of Presentation The accompanying condensed Parent only financial statements are required in accordance with Rule 4-08(e)(3) of Regulation S-X. The financial statements include the amounts of the Parent and its investment in its subsidiaries under the equity method and does not present the financial statements of the Parent and its subsidiaries on a consolidated basis. Under the equity method, investment in its subsidiaries is stated at cost plus contributions and equity in undistributed income (loss) of subsidiary less distributions received since the date of acquisition. These condensed Parent only financial statements should be read in conjunction with the Atkore Inc. consolidated financial statements and their accompanying notes. 3. Dividends and Distributions from Subsidiaries The Company received distributions of $491,033, $500,161, and $135,066 from its subsidiaries for the years ended September 30, 2023, September 30, 2022 and September 30, 2021, respectively. The distributions received in fiscal 2023, 2022 and 2021 were used to repurchase shares of the Company's common stock. These dividends were permissible under an exception to the net asset restrictions of the agreements governing AII's borrowings, which allow for dividend payments from AII to the Parent for the purpose of repurchasing shares of Parent's common stock.

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS	Sep. 30, 2023
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS	SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS (in thousands) Balance at Beginning of Year Additional (Charges)/Benefit to Income Write offs and Other Balance at End of Year Accounts Receivable Allowance for Current and Expected Credit Losses: For the fiscal year ended: 2023 $ (2,544) (770) (1,865) $ (5,179) 2022 $ (2,510) (1,276) 1,242 $ (2,544) 2021 $ (3,167) (339) 996 $ (2,510) Deferred Tax Valuation Allowance: For the fiscal year ended: 2023 $ (13,415) (44) (5,620) $ (19,079) 2022 $ (11,523) (5,265) 3,373 $ (13,415) 2021 $ (10,203) (2,190) 870 $ (11,523)

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Pay vs Performance Disclosure
Net Income (Loss) Attributable to Parent	$ 689,899	$ 913,434	$ 587,857

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended	12 Months Ended
Insider Trading Arrangements	Sep. 30, 2023 shares	Sep. 30, 2023 shares
Trading Arrangements, by Individual
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Bill Waltz [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		Bill Waltz, President and Chief Executive Officer, initiated a new Rule 10b5-1 trading arrangement on August 23, 2023. This trading arrangement has a selling start date of November 22, 2023 and a plan end date of March 8, 2024. Under the trading arrangement, 79,600 options, less any options exercised/shares sold pursuant to a preexisting 10b5-1 plan, are available to be exercised and net settled by the broker upon reaching pricing targets defined in the trading arrangement. Bylaw Amendments On November 13, 2023, the Board of Directors (the “Board”) of Atkore Inc. (the “Company”) adopted the Fourth Amended and Restated Bylaws (as amended and restated, the “Bylaws”), effective on such date. The changes to the Bylaws include the following: • Article I, Section 1.04 (Meetings of Stockholders—Notice of Meetings; Waiver of Notice). Revised to reflect amended Section 222(a) of the General Corporation Law of the State of Delaware (the “DGCL”), which sets out requirements for the notice of a stockholder meeting. • Article I, Section 1.06 (Meetings of Stockholders—Voting Lists). Revised to reflect amended Section 219(a) of the DGCL, which no longer requires the stockholder list to be made available for inspection during the stockholder meeting. • Article I, Section 1.09 (Meetings of Stockholders—Adjournment). Revised to reflect amended Section 222(c) of the DGCL, which expands the circumstances under which an adjourned meeting can be reconvened without requiring a new notice of meeting. • Article I, Section 1.12 (Meetings of Stockholders—Notice of Stockholder Proposals and Nominations). Updated to (1) clarify the time periods during which a stockholder may make additional or substitute nominations or proposals, (2) expand the scope of disclosures required by a stockholder seeking to nominate persons to be elected to the Board or submit proposals regarding other business at a meeting of stockholders to include information regarding the stockholder, the beneficial owner, if any, on whose behalf the nomination or proposal is made, or any of their respective affiliates or associates, and any others acting in concert with any of the foregoing, and any director nominee, as applicable, (3) establish the number of persons a stockholder may nominate for election to the Board and require a representation that such nominees intend to serve a full term on the Board, (4) require proposed director nominees to complete and submit a questionnaire requested by the Company, (5) enhance and clarify the procedural mechanics in connection with stockholder nominations and proposals, (6) address compliance by stockholders with Rule 14a-19 promulgated under the Securities Exchange Act of 1934, commonly referred to as the “universal proxy rule” and (7) reflect that any stockholder not acting on behalf of the Board by soliciting proxies from other stockholders must use a proxy card color other than white, which is reserved for the exclusive use by the Board. • Article II, Section 2.06 (Meetings of Stockholders—Notice of Meetings; Waiver of Notice). Revised to clarify that notice of a meeting of the Board may be given by electronic transmission. • Article V, Section 5.01 (Capital Stock—Certificates of Stock; Uncertificated Shares). Revised to provide that the stock of the Company shall be uncertificated, unless otherwise provided by the Board.
Name	Bill Waltz
Title	President and Chief Executive Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	August 23, 2023
Aggregate Available	79,600	79,600

BASIS OF PRESENTATION AND SUM_2

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying audited consolidated financial statements of the Company and all of its subsidiaries included herein have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”).
Fiscal Periods	Fiscal Periods
Use of Estimates	Use of Estimates
Revenue Recognition	Revenue Recognition — The Company’s revenue arrangements primarily consist of a single performance obligation to transfer promised goods which is satisfied at a point in time when title, risks and rewards of ownership, and subsequently control have transferred to the customer. This generally occurs when the product is shipped to the customer, with an immaterial amount of transactions in which control transfers upon delivery. The Company primarily offers assurance-type standard warranties that do not represent separate performance obligations. Under the Inflation Reduction Act of 2022 (“IRA”), the Company is eligible for tax credits related to the manufacturing and selling of components used in the solar energy industry, starting on January 1, 2023. These tax credits are transferable under the IRA when they meet certain criteria. When credits do not meet the transferability criteria, the benefit is recognized within income tax expense in accordance with ASC 740, “Income Taxes.” The Company concluded that the tax credits earned during fiscal 2023 are not transferable and as a result, the Company recognized the benefit of the fiscal 2023 tax credits in its income tax expense. The Company has contractual arrangements with some customers who purchase credit eligible components to transfer a portion of these tax credits to those customers. In instances where the Company has such arrangements, and the credits are not transferable, the Company may transfer the economic value of the agreed upon portion of the tax credits in a manner agreed upon between the Company and the customer. Pursuant to such contractual arrangements, if the tax credits are eligible for transfer and will be transferred to the customer, the Company identifies two separate performance obligations under these contracts with the first being to transfer the promised goods and the second being to transfer the defined portion of the tax credits earned. The Company allocates the total value of these transactions between the two performance obligations. As a result of this allocation, the Company recognizes a reduction to revenue, similar to a rebate. When the Company does not transfer credits but instead transfers only the economic value, there is only a single performance obligation to transfer the promised goods with transfer of the economic value of the credits recognized as a reduction of revenue. The solar tax credit receivable is recorded in Prepaid Expenses and Other Current Assets whereas the liability to transfer the defined portion of the tax credits or the economic value is recorded in Customer Liabilities. For the year ended September 30, 2023, the Company has recognized a reduction of revenue of $30,401 for the economic value of tax credits to be transferred and a year to date benefit to income tax expense of $39,493. As of September 30, 2023, the Company has a $30,401 liability for credits to be transferred or the economic value of the credits and a solar tax credit receivable of $39,493. As of September 30, 2023, all activity related to the solar tax credits is within the Safety & Infrastructure segment. The Company has certain arrangements that require it to estimate at the time of sale the amounts of variable consideration that should not be recorded as revenue as certain amounts are not expected to be collected from customers, as well as an estimate of the value of products to be returned. The Company principally relies on historical experience, specific customer agreements, and anticipated future trends to estimate these amounts at the time of sale and to reduce the transaction price. These arrangements include sales discounts and allowances, volume rebates, and returned goods. The Company records its obligations related to these items within the Customer Liabilities line on the balance sheet. The Company has elected to utilize certain practical expedients available under GAAP. The Company records amounts billed to customers for reimbursement of shipping and handling costs within revenue. Shipping and handling costs associated with outbound freight after control over a product has
Cost of Sales	Cost of Sales — The Company includes all costs directly related to the production of goods for sale in cost of sales in the statement of operations. These costs include direct material, direct labor, production related overheads, excess and obsolescence costs, lower of cost or market provisions, freight and distribution costs, and the depreciation and amortization of assets directly used in the production of goods for sale.
Selling, General and Administrative Expenses	Selling, General and Administrative Expenses — These amounts primarily include payroll-related expenses for both administrative and selling personnel, compensation expense from stock-based awards, restructuring-related charges, third-party professional services and transactional gains or losses for foreign currency transactions, excluding the foreign exchange exposure for intercompany loan transactions, which is included in Other (income) and expense, net.
Cash and Cash Equivalents	Cash and Cash Equivalents
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for current and expected credit losses — The Company carries its accounts receivable at their face amounts less an allowance for current and expected credit losses. The allowance for current and expected credit losses reflects the best estimate of current and expected losses inherent in the Company’s accounts receivable portfolio determined on the basis of historical experience, specific allowances for known troubled accounts and other available evidence.
Inventories	Inventories
Property, Plant and Equipment	Property, Plant and Equipment — Property, plant and equipment, net, is recorded at cost less accumulated depreciation. Maintenance and repair expenditures are charged to expense when incurred. Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets as follows: Buildings 4 to 40 years Building improvements 3 to 20 years Machinery and equipment 1 to 20 years Leasehold improvements Lesser of remaining term of the lease or useful life Software 2 to 10 years The internal and external costs incurred to develop internal use computer software during the application development stage of the implementation, including the design of the chosen path, are capitalized. Other costs, including expenses incurred during the preliminary project stage, training expenses, data conversion costs and expenses incurred in the post implementation stage are expensed in the period incurred. Capitalized costs are amortized ratably over the useful life of the software when the software becomes operational. Upgrades and enhancements to internal use software are capitalized
Business Combinations	Business Combinations — The Company accounts for business combinations using the acquisition method of accounting, which requires that once control is obtained, all the assets acquired and liabilities assumed, including amounts attributable to noncontrolling interests, are recorded at their respective fair values at the date of acquisition. The determination of fair values of identifiable assets and liabilities requires estimates and the use of valuation techniques when market value is not readily available. For intangible assets acquired in a business combination, the Company typically use the income method. Significant estimates in valuing certain intangible assets include, but are not limited to, the amount and timing of future cash flows, growth rates, discount rates and useful lives. The excess of the purchase price over fair values of identifiable assets and liabilities is recorded as goodwill
Long-Lived Asset and Finite - Lived Intangible Asset Impairments	Long-Lived Asset and Finite - Lived Intangible Asset Impairments — The Company reviews long-lived assets, including property, plant and equipment and finite-lived intangible assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of the asset may not be fully recoverable. The Company groups assets at the lowest level for which cash flows are separately identified in order to measure an impairment. Recoverability of an asset or asset group is first measured by a comparison of the carrying amount to its estimated undiscounted future cash flows expected to be generated by the asset or asset group. If the carrying amount exceeds its estimated undiscounted future cash flows, an impairment charge is recognized as the amount by which the carrying amount of the asset or asset group exceeds the estimated fair value. If impairment is determined to exist, any related impairment loss is calculated based on the estimated fair value. Impairment losses on assets to be disposed of or held for sale, if any, are based on the estimated proceeds to be received, less costs of disposal.
Goodwill and Indefinite-Lived Intangible Assets Impairments	Goodwill and Indefinite-Lived Intangible Asset Impairments — The Company assesses the recoverability of goodwill and indefinite-lived trade names on an annual basis in accordance with Accounting Standards Codification (“ASC”) 350 “Intangibles - Goodwill and Other.” The measurement date is the first day of the fourth fiscal quarter, or more frequently, if events or circumstances indicate that it is more likely than not that the fair value of a reporting unit or the respective indefinite-lived trade name is less than the carrying value. The Company can elect to perform a quantitative or qualitative test of impairment. For fiscal 2023, 2022, and 2021 the Company performed a quantitative impairment assessment for goodwill. The Company calculated the fair value of its six reporting units considering three valuation approaches: (a) the income approach; (b) the guideline public company method; and (c) the comparable transaction method. The income approach calculates the fair value of the reporting unit using a discounted cash flow approach. Internally forecasted future cash flows, which the Company believes reasonably approximate market participant assumptions, are discounted using a weighted average cost of capital (Discount Rate) developed for each reporting unit. The Discount Rate is developed using market observable inputs, as well as considering whether or not there is a measure of risk related to the specific reporting unit’s forecasted performance. The key uncertainties in these calculations are the assumptions used in determining the reporting unit’s forecasted future performance, including revenue growth and EBITDA margins, as well as the perceived risk associated with those forecasts. Fair value under the guideline public company method is determined for each reporting unit by applying market multiples for comparable public companies to the reporting unit’s financial results. Fair value under the comparable transaction method is determined based on exchange prices in actual transactions and on asking prices for controlling interests in public or private companies currently offered for sale by applying market multiples for comparable public companies to the unit’s financial results. The key uncertainties in the guideline public company method and the comparable transaction method calculations are the assumptions used in determining the reporting unit's comparable public companies, comparable transactions and the selection of the market multiples. As a result of the Company’s plans to exit its operations in Russia and expectation to sell the related business at a loss, the Company recognized a goodwill impairment of $1,721 that was allocated from the reporting unit on a relative fair value basis. With the exception of the impairment recorded to the expected sale of the Russia operations, the Company did not record any other goodwill impairments in fiscal 2023, 2022, and 2021.
Fair Value Measurements	Fair Value Measurements — Authoritative guidance for fair value measurements establishes a three-level hierarchy that ranks the quality and reliability of information used in developing fair value estimates. The hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. In cases where two or more levels of inputs are used to determine fair value, a financial instrument's level is determined based on the lowest level input that is considered significant to the fair value measurement in its entirety. The three levels of the fair value hierarchy are summarized as follows: Level 1-inputs are based upon quoted prices (unadjusted) in active markets for identical assets or liabilities which are accessible as of the measurement date. Level 2-inputs are based upon quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and model-derived valuations for the asset or liability that are derived principally from or corroborated by market data for which the primary inputs are observable, including forward interest rates, yield curves, credit risk and exchange rates.
Income Taxes and Uncertain Tax Positions	Income Taxes and Uncertain Tax Positions — The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and tax basis of assets and liabilities using enacted tax rates in effect for the year it is expected the differences will reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period of the enactment date. The Company periodically assesses the realizability of the deferred tax assets. In making this determination management considers all available evidence, both positive and negative, including earnings history, expectations of future taxable income and available tax planning strategies. A valuation allowance is recorded to reduce the Company’s deferred tax assets to the amount that is considered more likely than not to be realized. Changes in the required valuation allowance are recorded in income in the period such determination is made.
Leases	Leases The Company engages in leasing transactions to meet the needs of the business. The Company leases certain manufacturing facilities, warehouses and distribution centers, office space, forklifts, vehicles and other machinery and equipment. The determination to lease, rather than purchase, an asset is primarily contingent upon capital requirements, duration of the forecasted business investment, and asset availability. The Company determines if an arrangement is a lease at inception and all arrangements deemed to be leases are subject to an assessment to determine the classification between finance and operating leases. The Company's significant assumptions and judgments in determining whether a contract is or contains a lease include establishing whether the supplier has the ability to use other assets to fulfill its service or whether the terms of the agreement enable the Company to control the use of a dedicated property, plant and equipment asset during the contract term. In the majority of the Company's contracts where it must identify whether a lease is present, it is readily determinable that the Company controls the use of the assets and obtains substantially all of the economic benefit during the term of the contract. In those contracts where identification is not readily determinable, the Company has determined that the supplier has either the ability to use another asset to provide the service or the terms of the contract give the supplier the rights to operate the asset at its discretion during the term of the contract, in which case the arrangement would not constitute a lease. Right-of-use assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term as of the commencement date. The Company’s lease agreements have terms that include both lease and non-lease components. Lease component fees are included in the present value of future minimum lease payments. Conversely, non-lease components are not subject to capitalization and are expensed as incurred. Per ASC 842 “Leases,” the contractual interest rate is used to calculate the present value of the future minimum lease payments. However, the majority of the Company’s leases do not provide an implicit rate. Therefore, the Company's significant assumption and judgments in determining the discount rate include determining the incremental borrowing rate. The Company’s incremental borrowing rates are based on the term of the lease, the economic environment of the lease and the effect of collateralization. The valuation of the ROU asset also includes lease payments made in advance of the lease commencement date and initial direct costs incurred to secure the lease and is reduced for lease incentives. The lease terms include options to extend or terminate the lease when it is reasonably certain the Company will exercise the options. Leases with an initial term of 12 months or less are classified as short-term leases and are not recorded on the consolidated balance sheets. The lease expense for short-term leases is recognized on a straight-line basis over the lease term. The Company has certain leasing agreements, related to leased vehicles available to our sales personnel, that contain guaranteed residual value terms, which are not expected to be triggered. The Company’s leasing portfolio does not contain any material restrictive covenants.
Translation of Foreign Currency	Translation of Foreign Currency — For the Company's non-U.S. subsidiaries that report in a functional currency other than United States dollars, assets and liabilities are translated into United States dollars using period end exchange rates. Revenue and expenses are translated at the monthly average exchange rates in effect during the reporting period. Foreign currency translation adjustments are included as a component of accumulated other comprehensive loss within the consolidated statements of comprehensive income.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Atkore has not adopted any accounting standards in the current fiscal year. There are no accounting standards with adoption dates in the next fiscal year that are applicable to the Company.

BASIS OF PRESENTATION AND SUM_3

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Estimated Useful Lives	Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets as follows: Buildings 4 to 40 years Building improvements 3 to 20 years Machinery and equipment 1 to 20 years Leasehold improvements Lesser of remaining term of the lease or useful life Software 2 to 10 years As of September 30, 2023 and September 30, 2022, property, plant and equipment at cost and accumulated depreciation were as follows: (in thousands) September 30, 2023 September 30, 2022 Land $ 29,082 $ 22,113 Buildings and related improvements 182,760 172,633 Machinery and equipment 513,563 427,460 Leasehold improvements 15,910 10,512 Software 47,072 36,884 Construction in progress 206,311 99,491 Property, plant and equipment, at cost 994,698 769,093 Accumulated depreciation (435,657) (378,873) Property, plant and equipment, net $ 559,041 $ 390,220

LEASES (Tables)

LEASES (Tables)	12 Months Ended
LEASES (Tables)	Sep. 30, 2023
Leases [Abstract]
Assets and Liabilities, Leases	(in thousands) September 30, 2023 September 30, 2022 Assets Operating lease assets $ 117,966 $ 68,715 Finance lease assets 7,108 5,209 Right-of-use assets, at cost $ 125,074 $ 73,924 Less: accumulated amortization (4,327) (2,889) Right-of-use assets, net $ 120,747 $ 71,035 Liabilities Current liabilities: Current portion of operating lease liabilities $ 15,030 $ 12,777 Current portion of finance lease liabilities 1,200 1,012 Current lease obligations $ 16,230 $ 13,789 Noncurrent liabilities: Operating lease liabilities $ 104,047 $ 56,601 Finance lease liabilities 1,470 1,374 Long-term lease obligations $ 105,517 $ 57,975 Total lease obligations $ 121,747 $ 71,764
Lease, Cost	The following table summarizes lease costs by type of cost for the fiscal year ended September 30, 2023, and the fiscal year ended September 30, 2022. In the consolidated statements of operations, cost of sales and selling, general and administrative expenses included lease costs of $20,054 and $7,215 for the fiscal year ended September 30, 2023 and $15,583 and $3,732 for the fiscal year ended September 30, 2022. Fiscal year ended (in thousands) September 30, 2023 September 30, 2022 Amortization of right-of-use assets $ 21,540 $ 13,916 Interest on lease liabilities 131 71 Variable lease costs 3,146 2,471 Short term lease costs 2,451 2,857 Total lease costs $ 27,269 $ 19,315 Lease Term and Discount Rate Fiscal year ended September 30, 2023 September 30, 2022 Weighted-average remaining lease term (years) Operating leases 9.5 8.1 Finance leases 2.5 2.7 Weighted-average discount rate Operating leases 6.4 % 4.5 % Finance leases 4.6 % 3.0 %
Operating Lease, Liability, Maturity	The Company's maturity analysis of its lease liabilities as of September 30, 2023 is as follows: (in thousands) Financing Leases Operating Leases 2024 $ 1,369 $ 21,471 2025 1,003 19,557 2026 578 17,913 2027 131 16,026 2028 4 12,811 2029 and after — 54,418 Total lease payments $ 3,085 $ 142,195 Less: Interest (415) (23,118) Present value of lease liabilities $ 2,670 $ 119,077
Finance Lease, Liability, Maturity	The Company's maturity analysis of its lease liabilities as of September 30, 2023 is as follows: (in thousands) Financing Leases Operating Leases 2024 $ 1,369 $ 21,471 2025 1,003 19,557 2026 578 17,913 2027 131 16,026 2028 4 12,811 2029 and after — 54,418 Total lease payments $ 3,085 $ 142,195 Less: Interest (415) (23,118) Present value of lease liabilities $ 2,670 $ 119,077

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	12 Months Ended
ACQUISITIONS (Tables)	Sep. 30, 2023
Business Combination and Asset Acquisition [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table summarizes the Level 3 fair values assigned to the net assets acquired and liabilities assumed as of the acquisition date for fiscal 2022: (in thousands) United Poly Other Total Fair value of consideration transferred: Cash consideration $ 227,420 $ 93,044 $ 320,464 Purchase price payable — 12,628 12,628 Working Capital Adjustment — 668 668 Total consideration transferred $ 227,420 $ 106,340 $ 333,760 Fair value of assets acquired and liabilities assumed: Cash 11,514 126 11,640 Accounts receivable 23,679 9,291 32,970 Inventories 13,455 8,111 21,566 Intangible assets 128,840 54,330 183,170 Fixed assets 13,648 8,533 22,181 Accounts payable (11,940) (5,086) (17,026) Income taxes (15,542) (2,075) (17,617) Other (2,751) 245 (2,506) Net assets acquired 160,903 73,475 234,378 Excess purchase price attributed to goodwill acquired $ 66,517 $ 32,865 $ 99,382 (in thousands) FRE Composites Fair value of consideration transferred: Cash consideration $ 36,993 Fair value of assets acquired and liabilities assumed: Cash 437 Accounts receivable 2,163 Inventories 3,355 Intangible assets 18,300 Fixed assets 8,509 Accounts payable (1,186) Income Taxes (4,293) Other (240) Net assets acquired 27,045 Excess purchase price attributed to goodwill acquired $ 9,948
Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination	The following table summarizes the fair value of intangible assets as of the acquisition date: United Poly Other (in thousands) Fair Value Weighted Average Useful Life (Years) Fair Value Weighted Average Useful Life (Years) Customer relationships $ 111,700 11 $ 50,020 9 Other 17,140 8 4,310 8 Total intangible assets $ 128,840 $ 54,330 The following table summarizes the fair value of intangible assets as of the acquisition date: FRE Composites ($ in thousands) Fair Value Weighted Average Useful Life (Years) Customer relationships $ 14,700 12.0 Other 3,600 6.0 Total intangible assets $ 18,300
Schedule of Business Acquisition, Pro Forma Results of Operations	The following table presents unaudited pro forma results of operations for the Company and all companies acquired in fiscal 2022 as if those acquisitions had occurred on October 1, 2020. The results presented below are for the fiscal years ended: Fiscal year ended (in thousands) September 30, 2022 September 30, 2021 Pro forma net sales $ 4,060,993 $ 3,048,378 Pro forma net income 920,022 584,754

POSTRETIREMENT BENEFITS (Tables

POSTRETIREMENT BENEFITS (Tables)	12 Months Ended
POSTRETIREMENT BENEFITS (Tables)	Sep. 30, 2023
Retirement Benefits [Abstract]
Schedule of Net Periodic Benefit Cost	The net periodic cost for the periods presented was as follows: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Interest cost $ 5,175 $ 2,958 $ 2,729 Expected return on plan assets (5,027) (5,392) (6,424) Amortization of actuarial loss 667 631 1,327 Net periodic cost $ 815 $ (1,803) $ (2,368) The weighted-average assumptions used to determine net periodic pension cost during the period were as follow: September 30, 2023 September 30, 2022 September 30, 2021 Discount rate 5.4 % 2.7 % 2.5 % Expected return on plan assets 5.0 % 4.0 % 6.2 % Rate of compensation increase N/a N/a N/a
Schedule of Change in Benefit Obligations and Plan Assets	The change in the benefit obligations, plan assets and the amounts recognized on the consolidated balance sheets was as follows (in thousands): Change in benefit obligations: Balance as of September 30, 2021 $ 140,745 Interest cost 2,958 Actuarial loss (36,411) Benefits and administrative expenses paid (6,090) Balance as of September 30, 2022 101,202 Interest cost 5,175 Actuarial gain (4,882) Benefits and administrative expenses paid (6,165) Balance as of September 30, 2023 $ 95,330 Change in plan assets: Balance as of September 30, 2021 $ 138,056 Actual return on plan assets (28,230) Employer contributions 188 Benefits and administrative expenses paid (6,090) Balance as of September 30, 2022 103,925 Actual return on plan assets 7,463 Employer contributions 220 Benefits and administrative expenses paid (6,165) Balance as of September 30, 2023 $ 105,443 Funded status: Funded status as of September 30, 2022 $ 2,723 Funded status as of September 30, 2023 $ 10,113
Schedule of Amounts Recognized in Balance Sheet	(in thousands) September 30, 2023 September 30, 2022 Amounts recognized in the consolidated balance sheets consist of: Pension Non-Current Assets $ 10,113 $ 2,723 Pension liabilities — — Net amount recognized $ 10,113 $ 2,723 Amounts recognized in accumulated other comprehensive loss (before income taxes) consist of: Net actuarial loss $ (15,631) $ (23,616) Total loss recognized $ (15,631) $ (23,616) Weighted-average assumptions used to determine pension benefit obligations at year end: Discount rate 5.8 % 5.4 % Rate of compensation increase N/a N/a
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets	The following table summarizes the defined benefit pension plans with accumulated benefit obligations in excess of plan assets: (in thousands) September 30, 2023 September 30, 2022 Accumulated benefit obligation $ — $ — Fair value of plan assets — — The following table summarizes the defined benefit pension plans with projected benefit obligations in excess of plan assets: (in thousands) September 30, 2023 September 30, 2022 Projected benefit obligation $ — $ — Fair value of plan assets — —
Schedule of Allocation of Plan Assets	Pension plans have the following weighted-average asset allocations: Asset Category: September 30, 2023 September 30, 2022 Equity securities —% 50% Debt securities 54% 46% Cash and cash equivalents 46% 4% Total 100% 100% September 30, 2023 September 30, 2022 (in thousands) Level 1 Level 2 Total Level 1 Level 2 Total United States equity securities $ — $ — $ — $ 29,583 $ — $ 29,583 Non-U.S. equity securities — — — 22,913 — 22,913 Fixed income securities 21,119 35,733 56,852 22,639 24,794 47,433 Cash and cash equivalents 48,591 — 48,591 3,996 — 3,996 Total $ 69,710 $ 35,733 $ 105,443 $ 79,131 $ 24,794 $ 103,925
Schedule of Future Benefit Payments	Benefit payments, which reflect future expected service as appropriate, are expected to be paid in each fiscal year as follows: (in thousands) 2024 $ 6,912 2025 7,103 2026 7,263 2027 7,321 2028 7,349 2028 to 2032 36,909

STOCK INCENTIVE PLAN (Tables)

STOCK INCENTIVE PLAN (Tables)	12 Months Ended
STOCK INCENTIVE PLAN (Tables)	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Assumptions	The assumptions used in the Black-Scholes option pricing model to value the options granted were as follows: Fiscal Year Ended September 30, 2023 September 30, 2022 September 30, 2021 Expected dividend yield — % — % — % Expected volatility 51 % 49 % 59 % Range of risk-free interest rates 3.92 % 1.40 % 0.52% Range of expected option lives 6 years 6 years 6 years September 30, 2023 September 30, 2022 September 30, 2021 Expected dividend yield — % — % — % Expected volatility 68 % 63 % 61% - Risk free interest rates 4.15 % 0.83 % 0.21 % Expected life 3 years 3 years 3 years Fair value $121.52 $122.25 $33.80
Schedule of Stock Option Activity	Stock option activity for the period September 30, 2020 to September 30, 2023 was as follows: Shares Weighted-Average Exercise Price Weighted-Average Grant Date Fair Value Aggregate Intrinsic Value Weighted-Average Remaining Contractual Term (in years) Outstanding as of September 30, 2020 1,375 $ 15.66 $ 11,443 Granted 72 $ 29.80 Exercised (678) $ 12.30 $ 33,075 Forfeited — — Outstanding as of September 30, 2021 769 $ 19.95 $ 10.89 $ 51,441 Granted 42 $ 105.94 $ 49.39 Exercised (98) $ 12.58 $ 9.84 $ 8,703 Forfeited — — Outstanding as of September 30, 2022 713 $ 26.00 $ 13.29 $ 38,062 5.22 Granted 51 $ 101.66 $ 54.06 Exercised (74) $ 13.26 $ 9.56 $ 9,201 Forfeited — — Outstanding as of September 30, 2023 690 $ 32.93 $ 16.69 $ 80,152 9.75 Exercisable as of September 30, 2023 539 $ 23.45 $ 67,835 4.13
Schedule of Nonvested Share Activity	Changes to the Company’s nonvested RSU awards for the year ended September 30, 2023 were as follows: Shares Weighted-average grant-date fair value Nonvested as of September 30, 2020 405 $ 26.44 Granted 218 32.01 Vested (229) 23.78 Forfeited (10) 28.48 Nonvested as of September 30, 2021 384 30.30 Granted 100 103.94 Vested (208) 27.40 Forfeited (14) 49.23 Nonvested as of September 30, 2022 262 58.72 Granted 138 102.71 Vested (144) 47.43 Forfeited (10) 84.89 Nonvested as of September 30, 2023 246 $ 86.16 Changes to the Company’s non-vested PSU awards for the year ended September 30, 2023 were as follows: Shares Weighted-average grant-date fair value Nonvested as of September 30, 2020 425 $ 25.15 Granted 156 31.67 Vested (171) 21.55 Adjustment for achieved performance upon issuance 57 22.95 Forfeited (14) 29.43 Nonvested as of September 30, 2021 453 $ 28.07 Granted 52 113.51 Vested (381) 18.17 Adjustment for achieved performance upon issuance 190 18.17 Forfeited (1) 57.61 Nonvested as of September 30, 2022 313 $ 48.19 Granted 69 110.71 Vested (190) 39.94 Adjustment for achieved performance upon issuance 83 39.31 Forfeited (1) 31.67 Nonvested as of September 30, 2023 273 $ 67.02

OTHER (INCOME) AND EXPENSE, N_2

OTHER (INCOME) AND EXPENSE, NET (Tables)	12 Months Ended
OTHER (INCOME) AND EXPENSE, NET (Tables)	Sep. 30, 2023
Other Income, Nonoperating [Abstract]
Schedule of Other (Income) and Expense, Net	Other (income) and expense, net consisted of the following: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Gain on purchase of business $ — $ — $ (731) Undesignated foreign currency derivative instruments — (4,379) 2,201 Business interruption insurance recovery — — (15,500) Foreign exchange loss (gain) on intercompany loans (88) 5,342 (1,534) Pension-related expense (benefit) 579 (1,803) (2,368) Loss on assets held for sale 7,477 — — Other 1 350 (220) Other (income) and expense, net $ 7,969 $ (490) $ (18,152)

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
INCOME TAXES (Tables)	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Schedule of Components of Income (Loss) from Continuing Operations and Income Tax Expense	Significant components of income before income taxes and income tax expense for the fiscal years ended September 30, 2023, September 30, 2022 and September 30, 2021 consisted of the following: (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Components of income before income taxes: United States $ 817,853 $ 1,174,109 $ 770,350 Non-U.S 32,437 29,511 9,651 Income before income taxes $ 850,290 $ 1,203,620 $ 780,001 Income tax expense: Current: United States: Federal $ 110,714 $ 228,141 $ 182,105 State 25,556 49,793 46,913 Non-U.S: 11,261 9,198 6,432 Current income tax expense $ 147,531 $ 287,132 $ 235,450 Deferred: United States: Federal $ 12,670 $ 3,174 $ (35,442) State 1,274 753 (7,281) Non-U.S: (1,085) (873) (583) Deferred income (benefit) tax expense 12,860 3,054 (43,306) Income tax expense $ 160,391 $ 290,186 $ 192,144
Schedule of Federal Income Tax Rate and Effective Income Tax Rate Reconciliation	Differences between the statutory federal income tax rate and effective income tax rate are summarized below: (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Statutory federal tax 21 % 21 % 21 % Adjustments to reconcile to the effective income tax rate: State income taxes 3 % 3 % 4 % Stock-based compensation (1) % (1) % (1) % Solar tax credits (5) % — % — % Other 1 % 1 % 1 % Effective income tax rate 19 % 24 % 25 %
Schedule of Components of Net Deferred Income Tax Assets	The components of the net deferred income tax assets are as follows: (in thousands) September 30, 2023 September 30, 2022 Deferred tax assets: Accrued liabilities and reserves $ 42,824 $ 47,582 Tax loss and credit carryforwards 20,648 17,272 Postretirement benefits — 583 Inventory 21,256 29,501 Lease obligations 29,722 17,779 Other 4,686 1,079 $ 119,136 $ 113,796 Deferred tax liabilities: Property, plant and equipment $ (37,814) $ (28,475) Intangible assets (49,084) (56,886) Right-of-use assets, net (29,583) (17,095) Other (5,376) (4,156) $ (121,857) $ (106,612) Net deferred tax liability before valuation allowance (2,721) 7,184 Valuation allowance (19,079) (13,415) Net deferred tax liability $ (21,800) $ (6,231)
Schedule of Reconciliation of Unrecognized Tax Benefits, Excluding Interest and Penalties	A reconciliation of the beginning and ending amount of unrecognized tax benefit, excluding interest and penalties, is as follows: (in thousands) For the period from September 30, 2020 to September 30, 2023 Balance as of September 30, 2020 $ 1,614 Additions based on tax positions related to prior years 291 Additions based on tax positions related to current year 1,658 Settlements (230) Balance as of September 30, 2021 3,333 Additions based on tax positions related to prior years 322 Additions based on tax positions related to current year 342 Settlements (3,012) Balance as of September 30, 2022 985 Reductions based on tax positions related to prior years (75) Additions based on tax positions related to current year 1,792 Expiration of statute of limitations (121) Balance as of September 30, 2023 $ 2,581
Schedule of Tax Years Subject to Examination	The following tax years remain subject to examination by the major tax jurisdictions as follows: Jurisdiction Years Open to Audit United States 2020, 2021 and 2022

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
EARNINGS PER SHARE (Tables)	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted earnings per share: Fiscal Year Ended (in thousands, except per share data) September 30, 2023 September 30, 2022 September 30, 2021 Numerator: Net income $ 689,899 $ 913,434 $ 587,857 Less: Undistributed earnings allocated to participating securities 10,637 14,460 11,380 Net income available to common shareholders $ 679,262 $ 898,974 $ 576,477 Denominator: Basic weighted average common shares outstanding 38,797 43,717 46,569 Effect of dilutive securities: Non-participating employee stock options (1) 531 563 737 Diluted weighted average common shares outstanding 39,328 44,280 47,306 Basic earnings per share $ 17.51 $ 20.56 $ 12.38 Diluted earnings per share $ 17.27 $ 20.30 $ 12.19 (1) There were no Stock options to shares of common stock were outstanding during the years ended September 30, 2023, September 30, 2022, and September 30, 2021, respectively, Any options available would not be included in the calculation of diluted earnings per share as the impact of these would have been anti-dilutive.

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	12 Months Ended
ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	Sep. 30, 2023
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Loss	The following table presents the changes in accumulated other comprehensive loss by component, net of tax: (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of September 30, 2021 $ (19,318) $ (9,408) $ (28,726) Other comprehensive (loss) income before reclassifications 2,051 (23,943) (21,892) Amounts reclassified from accumulated other comprehensive loss 472 — 472 Net current period other comprehensive (loss) income 2,523 (23,943) (21,420) Balance as of September 30, 2022 $ (16,795) $ (33,351) $ (50,146) Other comprehensive income (loss) before reclassifications 5,493 10,212 15,705 Amounts reclassified from accumulated other comprehensive loss 501 — 501 Net current period other comprehensive income (loss) 5,994 10,212 16,206 Balance as of September 30, 2023 $ (10,801) $ (23,139) $ (33,940)
Reclassification out of Accumulated Other Comprehensive Income	The following is a summary of the amounts reclassified from accumulated other comprehensive loss to net income: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Amortization of defined benefit pension items: Amortization of net loss (included within other income, net) $ 667 $ 631 $ 1,327 Tax expense (166) (159) (337) Net reclassifications for the period $ 501 $ 472 $ 990

INVENTORIES, NET (Tables)

INVENTORIES, NET (Tables)	12 Months Ended
INVENTORIES, NET (Tables)	Sep. 30, 2023
Inventory Disclosure [Abstract]
Schedule of Inventory, Net	(in thousands) September 30, 2023 September 30, 2022 Purchased materials and manufactured parts, net $ 231,518 $ 166,038 Work in process, net 60,524 61,182 Finished goods, net 201,810 227,291 Inventories, net $ 493,852 $ 454,511

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	12 Months Ended
PROPERTY, PLANT AND EQUIPMENT (Tables)	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Depreciation is calculated using the straight-line method over the estimated useful lives of the related assets as follows: Buildings 4 to 40 years Building improvements 3 to 20 years Machinery and equipment 1 to 20 years Leasehold improvements Lesser of remaining term of the lease or useful life Software 2 to 10 years As of September 30, 2023 and September 30, 2022, property, plant and equipment at cost and accumulated depreciation were as follows: (in thousands) September 30, 2023 September 30, 2022 Land $ 29,082 $ 22,113 Buildings and related improvements 182,760 172,633 Machinery and equipment 513,563 427,460 Leasehold improvements 15,910 10,512 Software 47,072 36,884 Construction in progress 206,311 99,491 Property, plant and equipment, at cost 994,698 769,093 Accumulated depreciation (435,657) (378,873) Property, plant and equipment, net $ 559,041 $ 390,220

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
GOODWILL AND INTANGIBLE ASSETS (Tables)	Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Changes in the carrying amount of goodwill are as follows: Segment (in thousands) Electrical Safety & Infrastructure Total Balance as of September 30, 2021 $ 155,471 $ 43,577 $ 199,048 Goodwill acquired during year 87,964 9,431 97,395 Exchange rate effects (6,727) (386) (7,113) Balance as of September 30, 2022 $ 236,708 $ 52,622 $ 289,330 Goodwill acquired during year 18,669 14 18,683 Impairment (1,721) — (1,721) Other purchase accounting adjustments 1,989 — 1,989 Exchange rate effects 2,782 43 2,825 Balance as of September 30, 2023 $ 258,427 $ 52,679 $ 311,106
Schedule of Finite-Lived Intangible Assets	The following table provides the gross carrying value, accumulated amortization, and net carrying value for each major class of intangible assets: September 30, 2023 September 30, 2022 (in thousands) Weighted Average Useful Life (Years) Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Amortizable Intangible Assets: Customer relationships 11 $ 596,396 $ (318,058) $ 278,338 $ 532,768 $ (267,940) $ 264,828 Other 8 43,633 (20,406) 23,227 35,681 (10,602) 25,079 Total 640,029 (338,464) 301,565 568,449 (278,542) 289,907 Indefinite-lived Intangible Assets: Trade names 92,806 — 92,806 92,799 — 92,799 Total $ 732,835 $ (338,464) $ 394,372 $ 661,248 $ (278,542) $ 382,706
Schedule of Indefinite-Lived Intangible Assets	The following table provides the gross carrying value, accumulated amortization, and net carrying value for each major class of intangible assets: September 30, 2023 September 30, 2022 (in thousands) Weighted Average Useful Life (Years) Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Amortizable Intangible Assets: Customer relationships 11 $ 596,396 $ (318,058) $ 278,338 $ 532,768 $ (267,940) $ 264,828 Other 8 43,633 (20,406) 23,227 35,681 (10,602) 25,079 Total 640,029 (338,464) 301,565 568,449 (278,542) 289,907 Indefinite-lived Intangible Assets: Trade names 92,806 — 92,806 92,799 — 92,799 Total $ 732,835 $ (338,464) $ 394,372 $ 661,248 $ (278,542) $ 382,706
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Expected amortization expense for intangible assets over the next five years and thereafter is as follows (in thousands): 2024 $ 54,421 2025 43,341 2026 40,741 2027 39,621 2028 29,432 2029 and thereafter 94,009

DEBT (Tables)

DEBT (Tables)	12 Months Ended
DEBT (Tables)	Sep. 30, 2023
Debt Disclosure [Abstract]
Schedule of Debt	Debt as of September 30, 2023 and September 30, 2022 was as follows: (in thousands) September 30, 2023 September 30, 2022 New Senior Secured Term Loan Facility due May 26, 2028 $ 371,667 $ 371,381 Senior Notes Due June 1, 2031 400,000 400,000 ABL Credit Facility — — Deferred financing costs (8,980) (10,844) Long-term debt $ 762,687 $ 760,537
Schedule of Contractual Obligation Maturities of Long-Term, Fiscal Year Maturity	As of September 30, 2023, future contractual maturities of long-term debt are as follows (in thousands): 2024 $ — 2025 — 2026 — 2027 — 2028 373,000 2029 and thereafter 400,000 Total $ 773,000

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
FAIR VALUE MEASUREMENTS (Tables)	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	The following table presents the recurring assets and liabilities measured at fair value as of September 30, 2023 and September 30, 2022 in accordance with the fair value hierarchy: September 30, 2023 September 30, 2022 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Cash equivalents $ 321,282 $ — $ — $ 291,757 $ — $ — Forward currency contracts — — — — — — Liabilities Forward currency contracts — $ — — — $ — —
Estimated Fair Value of Financial Instruments Not Carried at Fair Value	The estimated fair value of financial instruments not carried at fair value in the consolidated balance sheets were as follows: September 30, 2023 September 30, 2022 (in thousands) Carrying Value Fair Value Carrying Value Fair Value New Senior Secured Term Loan Facility due May 26, 2028 $ 373,000 $ 372,068 $ 373,000 $ 370,203 Senior Notes due June 2031 400,000 334,368 400,000 318,912 Total debt $ 773,000 $ 706,436 $ 773,000 $ 689,115

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	12 Months Ended
SEGMENT INFORMATION (Tables)	Sep. 30, 2023
Segment Reporting [Abstract]
Schedule of Segment Information	Fiscal year ended September 30, 2023 September 30, 2022 September 30, 2021 (in thousands) External Net Sales Inter- segment Sales Adjusted EBITDA External Net Sales Inter- segment Sales Adjusted EBITDA External Net Sales Inter- segment Sales Adjusted EBITDA Electrical $ 2,675,050 $ 25 $ 1,004,853 $ 3,013,755 $ — $ 1,273,410 $ 2,229,862 $ 3,437 $ 873,868 Safety & Infrastructure 843,711 447 $ 103,231 900,194 394 $ 138,390 698,152 168 $ 81,827 Eliminations — (471) (394) — (3,605) Consolidated operations $ 3,518,761 $ — $ 3,913,949 $ — $ 2,928,014 $ — Capital Expenditures Total Assets (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 September 30, 2023 September 30, 2022 September 30, 2021 Electrical $ 137,485 $ 61,721 $ 34,995 $ 1,715,419 $ 1,524,670 $ 1,122,835 Safety & Infrastructure 69,475 38,280 22,407 753,821 618,331 482,942 Unallocated 11,928 35,775 7,072 465,769 455,995 604,322 Consolidated operations $ 218,888 $ 135,776 $ 64,474 $ 2,935,009 $ 2,598,996 $ 2,210,099 Presented below is a reconciliation of operating segment Adjusted EBITDA to Income before income taxes: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Operating segment Adjusted EBITDA Electrical $ 1,004,853 $ 1,273,410 $ 873,868 Safety & Infrastructure 103,231 138,390 81,827 Total $ 1,108,083 $ 1,411,800 $ 955,695 Unallocated expenses (a) (65,956) (70,010) (58,148) Depreciation and amortization (115,524) (84,415) (78,557) Interest expense, net (35,232) (30,676) (32,899) Loss on extinguishment of debt — — (4,202) Stock-based compensation (21,101) (17,245) (17,047) Transaction costs (968) (3,424) (667) Loss on assets held for sale (7,477) — — Other (b) (11,535) (2,410) 15,826 Income before income taxes $ 850,290 $ 1,203,620 $ 780,001 (a) Represents unallocated selling, general and administrative activities and associated expenses including, in part, executive, legal, finance, human resources, information technology, business development and communications, as well as certain costs and earnings of employee-related benefits plans, such as stock-based compensation and a portion of self-insured medical costs. (b) Represents other items, such as inventory reserves and adjustments, loss on disposal of property, plant and equipment, insurance recovery related to damages of property, plant and equipment, release of indemnified uncertain tax positions and realized or unrealized gain (loss) on foreign currency impacts of intercompany loans, restructuring charges, gain on purchase of business, impairment charges, and related forward currency derivatives. The Company’s long-lived assets and net sales by geography were as follows: Long-lived assets Net sales (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 September 30, 2023 September 30, 2022 September 30, 2021 United States $ 612,066 $ 410,263 $ 258,069 $ 3,150,143 $ 3,552,893 $ 2,637,118 Other Americas 8,655 7,195 6,180 94,064 102,626 53,151 Europe 52,498 38,396 45,917 228,885 213,581 183,985 Asia-Pacific 6,569 5,400 6,569 45,669 44,849 53,760 Total $ 679,788 $ 461,255 $ 316,735 $ 3,518,761 $ 3,913,949 $ 2,928,014 The table below shows the amount of net sales from external customers for each of the Company’s product categories which accounted for 10% or more of consolidated net sales in any of the last three fiscal years: Fiscal Year Ended (in thousands) September 30, 2023 September 30, 2022 September 30, 2021 Metal Electrical Conduit and Fittings $ 529,083 $ 635,481 $ 612,137 Plastic Pipe Conduit and Fittings 1,252,422 1,479,331 893,199 Electrical Cable and Flexible Conduit 506,994 535,194 424,411 Other Electrical products (a) 386,551 363,749 300,115 Electrical 2,675,050 3,013,755 2,229,862 Mechanical Tube 367,730 445,453 395,289 Other Safety & Infrastructure products (b) 475,982 454,741 302,863 Safety & Infrastructure 843,711 900,194 698,152 Net sales $ 3,518,761 $ 3,913,949 $ 2,928,014 (a) Other Electrical products includes International Cable Management, Fiberglass Conduit and Corrosion Resistant Conduit (b) Other S&I products includes Metal Framing and Fittings, Construction Services, Perimeter Security and Cable Management

BASIS OF PRESENTATION AND SUM_4

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Share Repurchase Program (Details)	Sep. 30, 2023 USD ($) vote	Nov. 11, 2022 USD ($)	Apr. 26, 2022 USD ($)	Nov. 16, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jan. 28, 2021 USD ($)	Dec. 25, 2020 USD ($)	Feb. 05, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of vote per share, common stock \| vote	1
Stock repurchase program, authorized amount		$ 1,300,000,000	$ 800,000,000	$ 400,000,000		$ 100,000,000		$ 50,000,000
Remaining authorized repurchase amount	$ 309,100,000,000				$ 0		$ 0

BASIS OF PRESENTATION AND SUM_5

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2023 USD ($)
Disaggregation of Revenue [Line Items]
Reduction of revenue for economic value of tax credits to be transferred	$ 30,401
Benefit to tax provision related to tax credits	39,493
Liability for credits to be transferred	30,401
Solar tax credit receivable	$ 39,493
Minimum
Disaggregation of Revenue [Line Items]
Performance obligation and payment period	30 days
Maximum
Disaggregation of Revenue [Line Items]
Performance obligation and payment period	60 days

BASIS OF PRESENTATION AND SUM_6

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant and Equipment (Details)	Sep. 30, 2023
Minimum \| Buildings
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	4 years
Minimum \| Building improvements
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	3 years
Minimum \| Machinery and equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	1 year
Minimum \| Software
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	2 years
Maximum \| Buildings
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	40 years
Maximum \| Building improvements
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	20 years
Maximum \| Machinery and equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	20 years
Maximum \| Software
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	10 years

BASIS OF PRESENTATION AND SUM_7

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Long-Lived Asset and Finite-Lived Intangible Asset Impairments (Details)	Sep. 30, 2023
Minimum \| Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	6 years
Minimum \| Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	1 year
Maximum \| Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	14 years
Maximum \| Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Useful Life (Years)	20 years

BASIS OF PRESENTATION AND SUM_8

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Goodwill and Indefinite-Lived Intangible Asset Impairments (Details)	12 Months Ended
	Sep. 30, 2023 USD ($) reportingUnit	Sep. 30, 2022 USD ($) reportingUnit	Sep. 30, 2021 USD ($) reportingUnit
Finite-Lived Intangible Assets [Line Items]
Number of reporting units \| reportingUnit	6	6	6
Goodwill impairment	$ 1,721,000
Impairment indefinite-lived asset	0	$ 0	$ 0
Russian Operations
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	1,721,000
All Other Reporting Units
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	0	$ 0	$ 0
Electrical
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 1,721,000

LEASES - Assets and Liabilities

LEASES - Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Assets
Operating lease assets	$ 117,966	$ 68,715
Operating lease, right-of-use asset, Statement of financial position [extensible enumeration]	Right-of-use assets, net	Right-of-use assets, net
Finance lease assets	$ 7,108	$ 5,209
Finance lease, right-of-use asset, statement of financial position [extensible enumeration]	Right-of-use assets, net	Right-of-use assets, net
Right-of-use assets, at cost	$ 125,074	$ 73,924
Less: accumulated amortization	(4,327)	(2,889)
Right-of-use assets, net	120,747	71,035
Current liabilities:
Current portion of operating lease liabilities	$ 15,030	$ 12,777
Operating lease, liability, current, statement of financial position [extensible list]	Current lease obligations	Current lease obligations
Current portion of finance lease liabilities	$ 1,200	$ 1,012
Finance lease, liability, current, statement of financial position [extensible enumeration]	Current lease obligations	Current lease obligations
Current lease obligations	$ 16,230	$ 13,789
Noncurrent liabilities:
Operating lease liabilities	$ 104,047	$ 56,601
Operating lease, liability, noncurrent, statement of financial position [extensible list]	Long-term lease obligations	Long-term lease obligations
Finance lease liabilities	$ 1,470	$ 1,374
Finance lease, liability, noncurrent, statement of financial position [extensible enumeration]	Long-term lease obligations	Long-term lease obligations
Long-term lease obligations	$ 105,517	$ 57,975
Total lease obligations	$ 121,747	$ 71,764

LEASES - Additional Information

LEASES - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease, cost	$ 27,269	$ 19,315
Cost of sales
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease, cost	20,054	15,583
Selling, General and Administrative Expenses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease, cost	$ 7,215	$ 3,732

LEASES - Lease Cost (Details)

LEASES - Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
LEASES - Lease Cost (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Leases [Abstract]
Amortization of right-of-use assets	$ 21,540	$ 13,916
Interest on lease liabilities	131	71
Variable lease costs	3,146	2,471
Short term lease costs	2,451	2,857
Total lease costs	$ 27,269	$ 19,315

LEASES - Maturity of Lease Liab

LEASES - Maturity of Lease Liabilities (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Financing Leases
2024	$ 1,369
2025	1,003
2026	578
2027	131
2028	4
2029 and after	0
Total lease payments	3,085
Less: Interest	(415)
Present value of lease liabilities	2,670
Operating Leases
2024	21,471
2025	19,557
2026	17,913
2027	16,026
2028	12,811
2029 and after	54,418
Total lease payments	142,195
Less: Interest	(23,118)
Present value of lease liabilities	$ 119,077

LEASES - Lease Term and Discoun

LEASES - Lease Term and Discount Rate (Details)	Sep. 30, 2023	Sep. 30, 2022
Weighted-average remaining lease term (years)
Operating leases	9 years 6 months	8 years 1 month 6 days
Finance leases	2 years 6 months	2 years 8 months 12 days
Weighted-average discount rate
Operating leases	6.40%	4.50%
Finance leases	4.60%	3%

ACQUISITIONS - Narrative (Detai

ACQUISITIONS - Narrative (Details) $ in Thousands

3 Months Ended

12 Months Ended

Nov. 07, 2022 USD ($)

Aug. 31, 2022 USD ($) acquiree

Jun. 22, 2022 USD ($)

May 19, 2022 USD ($)

Dec. 21, 2021 USD ($)

Dec. 20, 2021 USD ($)

Feb. 24, 2021 USD ($)

Oct. 22, 2020 USD ($)

Sep. 30, 2023 USD ($)

Sep. 30, 2022 USD ($)

Sep. 30, 2021 USD ($)

Business Acquisition [Line Items]

Goodwill

$ 311,106

$ 289,330

$ 199,048

Business acquisition, goodwill deductible for tax purposes

31,100

Selling, General and Administrative Expenses

Business Acquisition [Line Items]

Business acquisition-related expenses

$ 968

3,424

$ 667

Elite Polymer Solutions

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 90,230

Cash consideration

75,981

Purchase price payable

14,000

Purchase price paid subsequent to acquisition

$ 500

Goodwill

18,669

Identifiable intangible assets acquired

68,480

Working capital and other net tangible assets acquired

3,082

Elite Polymer Solutions | Customer relationships

Business Acquisition [Line Items]

Identifiable intangible assets acquired

$ 68,200

Weighted average useful life (years)

8 years

Cascade and Northwest Polymers

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 62,100

Cash consideration

52,738

Purchase price payable

$ 9,362

Business combination, number of acquiree | acquiree

Business acquisition, goodwill deductible for tax purposes

19,400

United Poly Systems, LLC

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 227,420

Cash consideration

227,420

Purchase price payable

Goodwill

$ 66,517

Business acquisition, goodwill deductible for tax purposes

$ 11,700

United Poly Systems, LLC | Customer relationships

Business Acquisition [Line Items]

Weighted average useful life (years)

11 years

Talon Products, LLC

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 4,193

Purchase price payable

$ 402

Four Star Industries LLC

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 23,195

Sasco Tubes & Roll Forming Inc

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 16,184

Cash consideration

13,320

Purchase price payable

$ 2,864

FRE Composites

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 36,993

Goodwill

9,948

Goodwill recognized

$ 1,600

FRE Composites | Customer relationships

Business Acquisition [Line Items]

Weighted average useful life (years)

12 years

Queen City Plastics

Business Acquisition [Line Items]

Purchase price of business acquisition

$ 6,214

ACQUISITIONS - Summary of Level

ACQUISITIONS - Summary of Level 3 Fair Values Assigned to Net Assets Acquired and Liabilities Assumed As of Acquisition Date (Details) - USD ($) $ in Thousands			12 Months Ended
	Jun. 22, 2022	Feb. 24, 2021	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2021
Fair value of assets acquired and liabilities assumed:
Excess purchase price attributed to goodwill acquired			$ 289,330	$ 311,106	$ 199,048
Fiscal 2022 Acquisitions
Fair value of consideration transferred:
Cash consideration			320,464
Purchase price payable			12,628
Working Capital Adjustment			668
Total consideration transferred			333,760
Fair value of assets acquired and liabilities assumed:
Cash			11,640
Accounts receivable			32,970
Inventories			21,566
Intangible assets			183,170
Fixed assets			22,181
Accounts payable			(17,026)
Income taxes			(17,617)
Other			(2,506)
Net assets acquired			234,378
Excess purchase price attributed to goodwill acquired			99,382
United Poly
Fair value of consideration transferred:
Cash consideration	$ 227,420
Purchase price payable	0
Working Capital Adjustment	0
Total consideration transferred	227,420
Fair value of assets acquired and liabilities assumed:
Cash	11,514
Accounts receivable	23,679
Inventories	13,455
Intangible assets	128,840
Fixed assets	13,648
Accounts payable	(11,940)
Income taxes	(15,542)
Other	(2,751)
Net assets acquired	160,903
Excess purchase price attributed to goodwill acquired	66,517
Other
Fair value of consideration transferred:
Cash consideration			93,044
Purchase price payable			12,628
Working Capital Adjustment			668
Total consideration transferred			106,340
Fair value of assets acquired and liabilities assumed:
Cash			126
Accounts receivable			9,291
Inventories			8,111
Intangible assets	$ 54,330		54,330
Fixed assets			8,533
Accounts payable			(5,086)
Income taxes			(2,075)
Other			245
Net assets acquired			73,475
Excess purchase price attributed to goodwill acquired			$ 32,865
FRE Composites
Fair value of consideration transferred:
Total consideration transferred		$ 36,993
Fair value of assets acquired and liabilities assumed:
Cash		437
Accounts receivable		2,163
Inventories		3,355
Intangible assets		18,300
Fixed assets		8,509
Accounts payable		(1,186)
Income taxes		(4,293)
Other		(240)
Net assets acquired		27,045
Excess purchase price attributed to goodwill acquired		$ 9,948

ACQUISITIONS - Summary of Fair

ACQUISITIONS - Summary of Fair Value as of Acquisition Date (Details) - USD ($) $ in Thousands	Jun. 22, 2022	Feb. 24, 2021	Sep. 30, 2022
United Poly
Business Acquisition [Line Items]
Intangible assets	$ 128,840
United Poly \| Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 111,700
Weighted Average Useful Life (Years)	11 years
United Poly \| Other
Business Acquisition [Line Items]
Intangible assets	$ 17,140
Weighted Average Useful Life (Years)	8 years
Other
Business Acquisition [Line Items]
Intangible assets	$ 54,330		$ 54,330
Other \| Customer relationships
Business Acquisition [Line Items]
Intangible assets	$ 50,020
Weighted Average Useful Life (Years)	9 years
Other \| Other
Business Acquisition [Line Items]
Intangible assets	$ 4,310
Weighted Average Useful Life (Years)	8 years
FRE Composites
Business Acquisition [Line Items]
Intangible assets		$ 18,300
FRE Composites \| Customer relationships
Business Acquisition [Line Items]
Intangible assets		$ 14,700
Weighted Average Useful Life (Years)		12 years
FRE Composites \| Other
Business Acquisition [Line Items]
Intangible assets		$ 3,600
Weighted Average Useful Life (Years)		6 years

ACQUISITIONS - Pro Forma Result

ACQUISITIONS - Pro Forma Results (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Business Combination and Asset Acquisition [Abstract]
Pro forma net sales	$ 4,060,993	$ 3,048,378
Pro forma net income	$ 920,022	$ 584,754

POSTRETIREMENT BENEFITS - Net P

POSTRETIREMENT BENEFITS - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Weighted-average assumptions used to determine net periodic pension cost during the period:
Discount rate	5.40%	2.70%	2.50%
Expected return on plan assets	5%	4%	6.20%
Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	$ 5,175	$ 2,958	$ 2,729
Expected return on plan assets	(5,027)	(5,392)	(6,424)
Amortization of actuarial loss	667	631	1,327
Net periodic cost	$ 815	$ (1,803)	$ (2,368)

POSTRETIREMENT BENEFITS - Chang

POSTRETIREMENT BENEFITS - Change in Benefit Obligations (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Change in benefit obligations:
Beginning balance, benefit obligations	$ 101,202	$ 140,745
Interest cost	5,175	2,958	$ 2,729
Actuarial loss	(4,882)	(36,411)
Benefits and administrative expenses paid	(6,165)	(6,090)
Ending balance, benefit obligations	95,330	101,202	140,745
Change in plan assets:
Beginning balance, fair value of plan assets	103,925	138,056
Actual return on plan assets	7,463	(28,230)
Employer contributions	220	188
Benefits and administrative expenses paid	(6,165)	(6,090)
Ending balance, fair value of plan assets	105,443	103,925	$ 138,056
Amounts recognized in the consolidated balance sheets consist of:
Pension Non-Current Assets	10,113	2,723
Pension liabilities	0	0
Net amount recognized	10,113	2,723
Amounts recognized in accumulated other comprehensive loss (before income taxes) consist of:
Net actuarial loss	(15,631)	(23,616)
Total loss recognized	$ (15,631)	$ (23,616)
Weighted-average assumptions used to determine pension benefit obligations at year end:
Discount rate	5.80%	5.40%

POSTRETIREMENT BENEFITS - Benef

POSTRETIREMENT BENEFITS - Benefit Obligation In Excess Of Plan Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Accumulated benefit obligation	$ 0	$ 0
Fair value of plan assets	0	0
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Projected benefit obligation	0	0
Fair value of plan assets	$ 0	$ 0

POSTRETIREMENT BENEFITS - Narra

POSTRETIREMENT BENEFITS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plans expense	$ 5,483	$ 4,615	$ 3,400
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations (as a percent)	100%	100%
Employer contributions	$ 220	$ 188
Estimated employer contributions in next fiscal year	279
Multiemployer Plan [Line Items]
Liability	$ 4,336	$ 4,685
Pension Plan \| Debt securities
Defined Benefit Plan Disclosure [Line Items]
Policy target allocation (as a percentage)	100%
Plan asset allocations (as a percent)	54%	46%
Pension Plan \| Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations (as a percent)	46%	4%

POSTRETIREMENT BENEFITS - Weigh

POSTRETIREMENT BENEFITS - Weighted-Average Asset Allocations (Details) - Pension Plan	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations (as a percent)	100%	100%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations (as a percent)	0%	50%
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations (as a percent)	54%	46%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations (as a percent)	46%	4%

POSTRETIREMENT BENEFITS - Asset

POSTRETIREMENT BENEFITS - Asset Allocations by Fair Value Hierarchy (Details) - Pension Plan - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 105,443	$ 103,925	$ 138,056
United States equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	29,583
Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	22,913
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	56,852	47,433
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48,591	3,996
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	69,710	79,131
Level 1 \| United States equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	29,583
Level 1 \| Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	22,913
Level 1 \| Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,119	22,639
Level 1 \| Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48,591	3,996
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35,733	24,794
Level 2 \| United States equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 \| Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 \| Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35,733	24,794
Level 2 \| Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

POSTRETIREMENT BENEFITS - Futur

POSTRETIREMENT BENEFITS - Future Expected Benefit Payments (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Retirement Benefits [Abstract]
2024	$ 6,912
2025	7,103
2026	7,263
2027	7,321
2028	7,349
2028 to 2032	$ 36,909

STOCK INCENTIVE PLAN - Narrativ

STOCK INCENTIVE PLAN - Narrative (Details) - USD ($) $ in Thousands, shares in Millions		12 Months Ended
	Nov. 21, 2019	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 21,101	$ 17,245	$ 17,047
Employee service share-based compensation, tax benefit from compensation expense		2,706	1,634	2,073
Selling, General and Administrative Expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 21,101	$ 17,245	$ 17,047
2020 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)	1.8
Life of awards	10 years

STOCK INCENTIVE PLAN - Stock Op

STOCK INCENTIVE PLAN - Stock Options Assumptions (Details) - Stock Options	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0%	0%	0%
Expected volatility	51%	49%	59%
Range of risk-free interest rates	3.92%	1.40%
Range of risk free interest rates, minimum			0.52%
Range of risk free interest rates, maximum
Range of expected option lives	6 years	6 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of expected option lives			6 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of expected option lives

STOCK INCENTIVE PLAN - Stock _2

STOCK INCENTIVE PLAN - Stock Options Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Shares
Outstanding, beginning balance (in shares)	713	769	1,375
Granted (in shares)	51	42	72
Exercised (in shares)	(74)	(98)	(678)
Forfeited (in shares)	0	0	0
Outstanding, ending balance (in shares)	690	713	769
Exercisable (in shares)	539
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 26	$ 19.95	$ 15.66
Granted (in dollars per share)	101.66	105.94	29.80
Exercised (in dollars per share)	13.26	12.58	12.30
Forfeited (in dollars per share)	0	0	0
Outstanding, ending balance (in dollars per share)	32.93	26	19.95
Exercisable (in dollars per share)	23.45
Stock Options, Additional Disclosures
Weighted average grant date fair value, options outstanding (in dollars per share)	16.69	13.29	$ 10.89
Weighted average grant date fair value of options granted (in dollars per share)	54.06	49.39
Weighted average grant date fair value of options exercised (in dollars per share)	$ 9.56	$ 9.84
Outstanding, aggregate intrinsic value	$ 80,152	$ 38,062	$ 51,441	$ 11,443
Exercised, aggregate intrinsic value	9,201	$ 8,703	$ 33,075
Exercisable, aggregate intrinsic value	$ 67,835
Outstanding, weighted average remaining contractual term (in years)	9 years 9 months	5 years 2 months 19 days
Exercisable, weighted average remaining contractual term (in years)	4 years 1 month 17 days

STOCK INCENTIVE PLAN - Stock _3

STOCK INCENTIVE PLAN - Stock Options Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock, net of taxes withheld	$ (14,428)	$ (24,045)	$ 2,660
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 1,117
Weighted-average period (years)	9 years 9 months 18 days
Fair value of shares vested	$ 1,924	1,447	1,465
Issuance of common stock, net of taxes withheld	973	1,230	8,535
Tax benefit for tax deductions from stock options exercised	$ 2,300	$ 2,176	$ 8,228

STOCK INCENTIVE PLAN - Restrict

STOCK INCENTIVE PLAN - Restricted Stock Narrative (Details) - Restricted Stock Units (RSUs) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (years)	3 years
Unrecognized compensation expense	$ 10,782
Weighted-average period (years)	1 year 4 months 13 days
Fair value of shares vested in period	$ 17,878	$ 20,342	$ 8,897

STOCK INCENTIVE PLAN - Schedule

STOCK INCENTIVE PLAN - Schedule of Nonvested Restricted Stock (Details) - Restricted Stock Units (RSUs) - $ / shares shares in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Shares
Nonvested, beginning balance (in shares)	262	384	405
Nonvested, granted (in shares)	138	100	218
Nonvested, vested (in shares)	(144)	(208)	(229)
Nonvested, forfeited (in shares)	(10)	(14)	(10)
Nonvested, ending balance (in shares)	246	262	384
Weighted-average grant-date fair value
Nonvested, beginning of year (in dollars per share)	$ 58.72	$ 30.30	$ 26.44
Nonvested, granted (in dollars per share)	102.71	103.94	32.01
Nonvested, vested (in dollars per share)	47.43	27.40	23.78
Nonvested, forfeited (in dollars per share)	84.89	49.23	28.48
Nonvested, ending of year (in dollars per share)	$ 86.16	$ 58.72	$ 30.30

STOCK INCENTIVE PLAN - Performa

STOCK INCENTIVE PLAN - Performance Share Units Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Closing stock price (in dollars per share)	$ 101.66	$ 105.94	$ 29.80
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance condition, percentage of the award and a market condition	70%
Performance condition, peer group, remaining percentage	30%
Award vesting period (years)	3 years
Unrecognized compensation expense	$ 5,228
Weighted-average period (years)	9 months 25 days

STOCK INCENTIVE PLAN - Perfor_2

STOCK INCENTIVE PLAN - Performance Share Assumptions (Details) - Performance Shares - $ / shares	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0%	0%	0%
Expected volatility	68%
Expected volatility, minimum		63%	61%
Expected volatility, maximum
Range of risk-free interest rates	4.15%	0.83%	0.21%
Expected life	3 years	3 years	3 years
Fair value (in dollars per share)	$ 121.52	$ 122.25	$ 33.80

STOCK INCENTIVE PLAN - Schedu_2

STOCK INCENTIVE PLAN - Schedule of Nonvested Performance Shares (Details) - Performance Shares - $ / shares shares in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Shares
Nonvested, beginning balance (in shares)	313	453	425
Shares issued (in shares)	69	52	156
Nonvested, vested (in shares)	(190)	(381)	(171)
Adjustment for achieved performance (in shares)	83	190	57
Nonvested, forfeited (in shares)	(1)	(1)	(14)
Nonvested, ending balance (in shares)	273	313	453
Weighted-average grant-date fair value
Nonvested, beginning of year (in dollars per share)	$ 48.19	$ 28.07	$ 25.15
Grant date fair value (in dollars per share)	110.71	113.51	31.67
Nonvested, vested (in dollars per share)	39.94	18.17	21.55
Adjustment for achieved performance (in dollars per share)	39.31	18.17	22.95
Nonvested, forfeited (in dollars per share)	31.67	57.61	29.43
Nonvested, ending of year (in dollars per share)	$ 67.02	$ 48.19	$ 28.07

OTHER (INCOME) AND EXPENSE, N_3

OTHER (INCOME) AND EXPENSE, NET (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Other Income, Nonoperating [Abstract]
Gain on purchase of business	$ 0	$ 0	$ (731)
Undesignated foreign currency derivative instruments	0	(4,379)	2,201
Business interruption insurance recovery	0	0	(15,500)
Foreign exchange loss (gain) on intercompany loans	(88)	5,342	(1,534)
Pension-related expense (benefit)	579	(1,803)	(2,368)
Loss on assets held for sale	7,477	0	0
Other	1	350	(220)
Other (income) and expense, net	$ 7,969	$ (490)	$ (18,152)

OTHER (INCOME) AND EXPENSE, N_4

OTHER (INCOME) AND EXPENSE, NET - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Other Income, Nonoperating [Abstract]
Loss on assets held for sale	$ 7,477	$ 0	$ 0

INCOME TAXES - Components of In

INCOME TAXES - Components of Income (Loss) from Continuing Operations and Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Components of income before income taxes:
United States	$ 817,853	$ 1,174,109	$ 770,350
Non-U.S	32,437	29,511	9,651
Income before income taxes	850,290	1,203,620	780,001
United States:
Federal	110,714	228,141	182,105
State	25,556	49,793	46,913
Non-U.S:	11,261	9,198	6,432
Current income tax expense	147,531	287,132	235,450
United States:
Federal	12,670	3,174	(35,442)
State	1,274	753	(7,281)
Non-U.S:	(1,085)	(873)	(583)
Deferred income (benefit) tax expense	12,860	3,054	(43,306)
Income tax expense	$ 160,391	$ 290,186	$ 192,144

INCOME TAXES - Differences Betw

INCOME TAXES - Differences Between Federal Income Tax Rate and Effective Income Tax Rate (Details)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Statutory federal tax	21%	21%	21%
Adjustments to reconcile to the effective income tax rate:
State income taxes	3%	3%	4%
Stock-based compensation	(1.00%)	(1.00%)	(1.00%)
Solar tax credits	(5.00%)	0%	0%
Other	1%	1%	1%
Effective income tax rate	19%	24%	25%

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Operating Loss Carryforwards [Line Items]
State income tax expense	$ 21,630	$ 39,759	$ 30,680
Solar tax credits	39,493
Limitations on executive compensation		6,996	2,587
Excess tax benefit from share-based compensation		11,438	7,352
Current year valuation allowance expense			2,190
Unrecognized tax benefits	2,581	985	3,333	$ 1,614
Accrued interest and penalties	236	77
Unrecognized tax benefits, increase (decrease)	1,792	(3,012)	1,949
Increase (decrease) of unrecognized tax benefits related to various state jurisdictions' uncertain tax positions	(196)	664	(230)
Increase (decrease) of accrued penalties and interest for uncertain tax positions	158	$ (183)	$ 72
Effective income tax rate reconciliation, foreign income tax rate differential, amount	98
Undistributed income	131,056
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carrying forwards	7,744
State
Operating Loss Carryforwards [Line Items]
Operating loss carrying forwards	23,599
Non-U.S.
Operating Loss Carryforwards [Line Items]
Operating loss carrying forwards	$ 68,189
Operating loss carryforwards expiration term (year)	5 years

INCOME TAXES - Components of Ne

INCOME TAXES - Components of Net Deferred Income Tax Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Deferred tax assets:
Accrued liabilities and reserves	$ 42,824	$ 47,582
Tax loss and credit carryforwards	20,648	17,272
Postretirement benefits	0	583
Inventory	21,256	29,501
Lease obligations	29,722	17,779
Other	4,686	1,079
Deferred tax assets	119,136	113,796
Deferred tax liabilities:
Property, plant and equipment	(37,814)	(28,475)
Intangible assets	(49,084)	(56,886)
Right-of-use assets, net	(29,583)	(17,095)
Other	(5,376)	(4,156)
Deferred tax liabilities	(121,857)	(106,612)
Net deferred tax liability before valuation allowance	(2,721)	7,184
Valuation allowance	(19,079)	(13,415)
Net deferred tax liability	$ (21,800)	$ (6,231)

INCOME TAXES - Unrecognized Tax

INCOME TAXES - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 985	$ 3,333	$ 1,614
Additions based on tax positions related to prior years		322	291
Additions based on tax positions related to current year	1,792	342	1,658
Reductions based on tax positions related to prior years	(75)
Settlements		(3,012)	(230)
Expiration of statute of limitations	(121)
Ending balance	$ 2,581	$ 985	$ 3,333

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net income	$ 689,899	$ 913,434	$ 587,857
Less: Undistributed earnings allocated to participating securities	10,637	14,460	11,380
Net income available to common shareholders, basic	679,262	898,974	576,477
Net income available to common shareholders, diluted	$ 679,262	$ 898,974	$ 576,477
Denominator:
Basic weighted average common shares (in shares)	38,797,000	43,717,000	46,569,000
Effect of dilutive securities: Non-participating employee stock options (in shares)	531,000	563,000	737,000
Diluted weighted average common shares outstanding (in shares)	39,328,000	44,280,000	47,306,000
Basic earnings per share (in dollars per share)	$ 17.51	$ 20.56	$ 12.38
Diluted earnings per share (in dollars per share)	$ 17.27	$ 20.30	$ 12.19
Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	0	0	0

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Change in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,249,787	$ 864,736	$ 378,410
Other comprehensive (loss) income before reclassifications	15,705	(21,892)
Amounts reclassified from accumulated other comprehensive loss	501	472
Total other comprehensive (loss) income	16,206	(21,420)	13,828
Balance at end of period	1,468,119	1,249,787	864,736
Defined benefit pension items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(16,795)	(19,318)
Other comprehensive (loss) income before reclassifications	5,493	2,051
Amounts reclassified from accumulated other comprehensive loss	501	472	990
Total other comprehensive (loss) income	5,994	2,523
Balance at end of period	(10,801)	(16,795)	(19,318)
Currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(33,351)	(9,408)
Other comprehensive (loss) income before reclassifications	10,212	(23,943)
Amounts reclassified from accumulated other comprehensive loss	0	0
Total other comprehensive (loss) income	10,212	(23,943)
Balance at end of period	(23,139)	(33,351)	(9,408)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(50,146)	(28,726)	(42,554)
Total other comprehensive (loss) income	16,206	(21,420)	13,828
Balance at end of period	$ (33,940)	$ (50,146)	$ (28,726)

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Amounts Reclassified (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net reclassifications for the period	$ 501	$ 472
Defined benefit pension items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net loss (included within other income, net)	667	631	$ 1,327
Tax expense	(166)	(159)	(337)
Net reclassifications for the period	$ 501	$ 472	$ 990

INVENTORIES, NET - Narrative (D

INVENTORIES, NET - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Inventory Disclosure [Abstract]
Inventories at lower of LIFO cost or market	82%	82%
FIFO inventory, higher than reported	$ 29,826	$ 64,550
Effect of LIFO inventory liquidation on operating income	2,394	248
Excess and obsolete inventory reserve	$ 25,585	$ 18,996

INVENTORIES, NET - Schedule of

INVENTORIES, NET - Schedule of Company Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Inventory Disclosure [Abstract]
Purchased materials and manufactured parts, net	$ 231,518	$ 166,038
Work in process, net	60,524	61,182
Finished goods, net	201,810	227,291
Inventories, net	$ 493,852	$ 454,511

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	$ 994,698	$ 769,093
Accumulated depreciation	(435,657)	(378,873)
Property, plant and equipment, net	559,041	390,220
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	29,082	22,113
Buildings and related improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	182,760	172,633
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	513,563	427,460
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	15,910	10,512
Software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	47,072	36,884
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	$ 206,311	$ 99,491

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 57,720	$ 48,239	$ 44,913

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Goodwill [Roll Forward]
Balance at beginning of period	$ 289,330	$ 199,048
Goodwill acquired during year	18,683	97,395
Impairment	(1,721)
Other purchase accounting adjustments	1,989
Exchange rate effects	2,825	(7,113)
Balance at end of period	311,106	289,330
Electrical
Goodwill [Roll Forward]
Balance at beginning of period	236,708	155,471
Goodwill acquired during year	18,669	87,964
Impairment	(1,721)
Other purchase accounting adjustments	1,989
Exchange rate effects	2,782	(6,727)
Balance at end of period	258,427	236,708
Safety & Infrastructure
Goodwill [Roll Forward]
Balance at beginning of period	52,622	43,577
Goodwill acquired during year	14	9,431
Impairment	0
Other purchase accounting adjustments	0
Exchange rate effects	43	(386)
Balance at end of period	$ 52,679	$ 52,622

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Indefinite-lived Intangible Assets [Line Items]
Loss on assets held for sale	$ 7,477	$ 0	$ 0
Goodwill impairment	1,721
Amortization expense	57,804	36,176	$ 33,644
Electrical
Indefinite-lived Intangible Assets [Line Items]
Accumulated impairment loss	5,645
Goodwill impairment	1,721
Safety & Infrastructure
Indefinite-lived Intangible Assets [Line Items]
Accumulated impairment loss		$ 43,000
Goodwill impairment	$ 0

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS - Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Amortizable intangible assets:
Gross Carrying Value	$ 640,029	$ 568,449
Accumulated Amortization	(338,464)	(278,542)
Net Carrying Value	301,565	289,907
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross Carrying Value	732,835	661,248
Net Carrying Value	394,372	382,706
Trade names
Indefinite-lived Intangible Assets [Line Items]
Trade names	92,806	92,799
Customer relationships
Amortizable intangible assets:
Gross Carrying Value	596,396	532,768
Accumulated Amortization	(318,058)	(267,940)
Net Carrying Value	$ 278,338	264,828
Customer relationships \| Weighted Average
Amortizable intangible assets:
Weighted Average Useful Life (Years)	11 years
Other
Amortizable intangible assets:
Gross Carrying Value	$ 43,633	35,681
Accumulated Amortization	(20,406)	(10,602)
Net Carrying Value	$ 23,227	$ 25,079
Other \| Weighted Average
Amortizable intangible assets:
Weighted Average Useful Life (Years)	8 years

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS - Expected Amortization Expense (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2024	$ 54,421
2025	43,341
2026	40,741
2027	39,621
2028	29,432
2029 and thereafter	$ 94,009

DEBT - Schedule of Debt (Detail

DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Deferred financing costs	$ (8,980)	$ (10,844)
Long-term debt	762,687	760,537
Secured Debt \| New Senior Secured Term Loan Facility due May 26, 2028
Debt Instrument [Line Items]
Carrying Value	371,667	371,381
Secured Debt \| Senior Notes Due June 1, 2031
Debt Instrument [Line Items]
Carrying Value	400,000	400,000
Secured Debt \| ABL Credit Facility
Debt Instrument [Line Items]
Carrying Value	$ 0	$ 0

DEBT - First Lien Loan - Narrat

DEBT - First Lien Loan - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Repayments of long-term debt	$ 0	$ 0	$ 835,120
Atkore International \| New Senior Secured Term Loan Facility due May 26, 2028 \| Secured Debt
Debt Instrument [Line Items]
Repayments of long-term debt			$ 26,000

DEBT - Contractual Obligation M

DEBT - Contractual Obligation Maturities of Long-Term, Fiscal Year Maturity (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Debt Disclosure [Abstract]
2024	$ 0
2025	0
2026	0
2027	0
2028	373,000
2029 and thereafter	400,000
Total	$ 773,000

DEBT - Senior Notes - Narrative

DEBT - Senior Notes - Narrative (Details) - Senior Notes - Senior Notes due June 2031	May 26, 2021 USD ($)
Debt Instrument [Line Items]
Debt instrument, face amount	$ 400,000,000
Debt instrument, interest rate, stated percentage	4.25%

DEBT - New Senior Secured Term

DEBT - New Senior Secured Term Loan Facility - Narrative (Details) - Secured Debt - Senior Term Loan Facility Due May 26, 2028 - USD ($)	Mar. 15, 2023	May 26, 2021
Debt Instrument [Line Items]
Debt instrument, face amount		$ 400,000,000
Debt instrument, annual amortization rate		1%
LIBOR
Debt Instrument [Line Items]
LIBOR floor rate (%)		0.50%
Debt instrument, basis spread on variable rate		2%
Alternate Base Rate
Debt Instrument [Line Items]
LIBOR floor rate (%)		1.50%
Debt instrument, basis spread on variable rate		1%
Secured Overnight Financing Rate SOFR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	2%
Secured Overnight Financing Rate SOFR \| Debt Instrument, Interest Period One
Debt Instrument [Line Items]
Credit spread adjustment	0.11448%
Secured Overnight Financing Rate SOFR \| Debt Instrument, Interest Period Two
Debt Instrument [Line Items]
Credit spread adjustment	0.26161%
Secured Overnight Financing Rate SOFR \| Debt Instrument, Interest Period Three
Debt Instrument [Line Items]
Credit spread adjustment	0.42826%

DEBT - ABL Credit Facility - Na

DEBT - ABL Credit Facility - Narrative (Details) - USD ($)				12 Months Ended
DEBT - ABL Credit Facility - Narrative (Details) - USD ($)	Mar. 24, 2023	May 26, 2021	Aug. 28, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt				$ 0	$ 0	$ (4,202,000)	$ (273,000)
Domestic Line of Credit \| Amended ABL Credit Facility \| LIBOR \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.25%
Domestic Line of Credit \| Amended ABL Credit Facility \| LIBOR \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.75%
Domestic Line of Credit \| Amended ABL Credit Facility \| Alternate Base Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.25%
Domestic Line of Credit \| Amended ABL Credit Facility \| Alternate Base Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.75%
Domestic Line of Credit \| Amended ABL Credit Facility \| Secured Overnight Financing Rate SOFR
Debt Instrument [Line Items]
Credit spread adjustment	0.10%
Domestic Line of Credit \| Amended ABL Credit Facility \| Secured Overnight Financing Rate SOFR \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.25%
Domestic Line of Credit \| Amended ABL Credit Facility \| Secured Overnight Financing Rate SOFR \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.75%
Foreign Line of Credit \| Amended ABL Credit Facility \| Line Of Credit Facility, Commitment Option One
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage		0.375%
Foreign Line of Credit \| Amended ABL Credit Facility \| Line Of Credit Facility, Commitment Option Two
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage		0.30%
Foreign Line of Credit \| Amended ABL Credit Facility \| Line Of Credit Facility, Commitment Option Three
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage		0.25%
Foreign Line of Credit \| Amended ABL Credit Facility \| Bankers Acceptance Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.25%
Foreign Line of Credit \| Amended ABL Credit Facility \| Bankers Acceptance Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.75%
Foreign Line of Credit \| Amended ABL Credit Facility \| Prime Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.25%
Foreign Line of Credit \| Amended ABL Credit Facility \| Prime Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.75%
Line of Credit \| Amended ABL Credit Facility \| Secured Debt
Debt Instrument [Line Items]
Debt instrument, extended term, period from amendment date		5 years
Debt instrument, extended term, period prior to maturity date		91 days
Line of credit facility, term, outstanding obligations threshold amount		$ 100,000,000
Atkore International \| Domestic Line of Credit \| ABL Credit Facility \| LIBOR \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.75%
Atkore International \| Domestic Line of Credit \| ABL Credit Facility \| LIBOR \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			2.25%
Atkore International \| Domestic Line of Credit \| ABL Credit Facility \| Alternate Base Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.75%
Atkore International \| Domestic Line of Credit \| ABL Credit Facility \| Alternate Base Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.25%
Atkore International \| Foreign Line of Credit \| ABL Credit Facility
Debt Instrument [Line Items]
Line of credit facility, unused capacity, commitment fee percentage			0.375%
Atkore International \| Foreign Line of Credit \| ABL Credit Facility \| Bankers Acceptance Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.75%
Atkore International \| Foreign Line of Credit \| ABL Credit Facility \| Bankers Acceptance Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			2.25%
Atkore International \| Foreign Line of Credit \| ABL Credit Facility \| Prime Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.75%
Atkore International \| Foreign Line of Credit \| ABL Credit Facility \| Prime Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.25%
Atkore International \| Line of Credit \| Amended ABL Credit Facility
Debt Instrument [Line Items]
Aggregate commitments				325,000,000
Credit availability				$ 322,406,000	312,095,000
Borrowing base percentage of eligible accounts receivable (%)				85%
Borrowing base percentage of eligible inventory (plus) (%)				80%
Debt instrument, covenant, borrowing base, percentage of inventory subject to certain limitations (%)				85%
Borrowings outstanding				$ 0	$ 0

DEBT - Use of Proceeds - Narrat

DEBT - Use of Proceeds - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	May 26, 2021	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Loss on extinguishment of debt		$ 0	$ 0	$ 4,202	$ 273
First Lien Term Loan Facility due December 22, 2023 \| Secured Debt
Debt Instrument [Line Items]
Repayments of debt	$ 772,000
Repayment of debt interest	4,000
Loss on extinguishment of debt	$ 4,200

FAIR VALUE MEASUREMENTS - Narra

FAIR VALUE MEASUREMENTS - Narrative (Details)	Sep. 30, 2021 GBP (£)
Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Notional Amount	£ 37,400,000

FAIR VALUE MEASUREMENTS - Asset

FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Level 1
Assets
Cash equivalents	$ 321,282	$ 291,757
Forward currency contracts	0	0
Liabilities
Forward currency contracts	0	0
Level 2
Assets
Cash equivalents	0	0
Forward currency contracts	0	0
Liabilities
Forward currency contracts	0	0
Level 3
Assets
Cash equivalents	0	0
Forward currency contracts	0	0
Liabilities
Forward currency contracts	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Estim

FAIR VALUE MEASUREMENTS - Estimated Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 773,000
Secured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	773,000	$ 773,000
Fair Value	706,436	689,115
Secured Debt \| New Senior Secured Term Loan Facility due May 26, 2028
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	373,000	373,000
Fair Value	372,068	370,203
Secured Debt \| Senior Notes due June 2031
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	400,000	400,000
Fair Value	$ 334,368	$ 318,912

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Loss Contingencies [Line Items]
Purchase obligation for fiscal 2023	$ 127,756
Purchase obligation for fiscal 2024	3,816
Purchase obligation thereafter	4,800
Business interruption insurance recovery	0	$ 0	$ 15,500
Minimum
Loss Contingencies [Line Items]
Probable losses	1,000
Maximum
Loss Contingencies [Line Items]
Probable losses	$ 8,000

GUARANTEES (Details)

GUARANTEES (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Workers' Compensation and General Liability Insurance Policies
Guarantor Obligations [Line Items]
Guarantees	$ 2,594
Surety Bond
Guarantor Obligations [Line Items]
Guarantees	$ 37,087

SEGMENT INFORMATION - Schedule

SEGMENT INFORMATION - Schedule of Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Net sales	$ 3,518,761	$ 3,913,949	$ 2,928,014
Capital Expenditures	218,888	135,776	64,474
Total Assets	2,935,009	2,598,996	2,210,099
Electrical
Segment Reporting Information [Line Items]
Net sales	2,675,050	3,013,755	2,229,862
Safety & Infrastructure
Segment Reporting Information [Line Items]
Net sales	843,711	900,194	698,152
Operating Segments
Segment Reporting Information [Line Items]
Net sales	3,518,761	3,913,949	2,928,014
Adjusted EBITDA	1,108,083	1,411,800	955,695
Operating Segments \| Electrical
Segment Reporting Information [Line Items]
Net sales	2,675,050	3,013,755	2,229,862
Adjusted EBITDA	1,004,853	1,273,410	873,868
Capital Expenditures	137,485	61,721	34,995
Total Assets	1,715,419	1,524,670	1,122,835
Operating Segments \| Safety & Infrastructure
Segment Reporting Information [Line Items]
Net sales	843,711	900,194	698,152
Adjusted EBITDA	103,231	138,390	81,827
Capital Expenditures	69,475	38,280	22,407
Total Assets	753,821	618,331	482,942
Intersegment Sales
Segment Reporting Information [Line Items]
Net sales	(471)	(394)	(3,605)
Intersegment Sales \| Electrical
Segment Reporting Information [Line Items]
Net sales	25	0	3,437
Intersegment Sales \| Safety & Infrastructure
Segment Reporting Information [Line Items]
Net sales	447	394	168
Unallocated
Segment Reporting Information [Line Items]
Capital Expenditures	11,928	35,775	7,072
Total Assets	$ 465,769	$ 455,995	$ 604,322

SEGMENT INFORMATION - Reconcili

SEGMENT INFORMATION - Reconciliation of Operating Segment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Unallocated expenses	$ (65,956)	$ (70,010)	$ (58,148)
Depreciation and amortization	(115,524)	(84,415)	(78,557)
Interest expense, net	(35,232)	(30,676)	(32,899)
Loss on extinguishment of debt	0	0	(4,202)	$ (273)
Stock-based compensation	(21,101)	(17,245)	(17,047)
Transaction costs	(968)	(3,424)	(667)
Loss on assets held for sale	(7,477)	0	0
Other	(11,535)	(2,410)	15,826
Income before income taxes	850,290	1,203,620	780,001
Operating Segments
Segment Reporting Information [Line Items]
Adjusted EBITDA	1,108,083	1,411,800	955,695
Operating Segments \| Electrical
Segment Reporting Information [Line Items]
Adjusted EBITDA	1,004,853	1,273,410	873,868
Operating Segments \| Safety & Infrastructure
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 103,231	$ 138,390	$ 81,827

SEGMENT INFORMATION - Schedul_2

SEGMENT INFORMATION - Schedule of Long-lived Assets and Net Sales By Geography (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 679,788	$ 461,255	$ 316,735
Net sales	3,518,761	3,913,949	2,928,014
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	612,066	410,263	258,069
Net sales	3,150,143	3,552,893	2,637,118
Other Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	8,655	7,195	6,180
Net sales	94,064	102,626	53,151
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	52,498	38,396	45,917
Net sales	228,885	213,581	183,985
Asia-Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	6,569	5,400	6,569
Net sales	$ 45,669	$ 44,849	$ 53,760

SEGMENT INFORMATION - Schedul_3

SEGMENT INFORMATION - Schedule of Net Sales From External Customers by Product Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Revenue from External Customer [Line Items]
Net sales	$ 3,518,761	$ 3,913,949	$ 2,928,014
Electrical
Revenue from External Customer [Line Items]
Net sales	2,675,050	3,013,755	2,229,862
Electrical \| Metal Electrical Conduit and Fittings
Revenue from External Customer [Line Items]
Net sales	529,083	635,481	612,137
Electrical \| Plastic Pipe Conduit and Fittings
Revenue from External Customer [Line Items]
Net sales	1,252,422	1,479,331	893,199
Electrical \| Electrical Cable and Flexible Conduit
Revenue from External Customer [Line Items]
Net sales	506,994	535,194	424,411
Electrical \| Other Electrical products
Revenue from External Customer [Line Items]
Net sales	386,551	363,749	300,115
Safety & Infrastructure
Revenue from External Customer [Line Items]
Net sales	843,711	900,194	698,152
Safety & Infrastructure \| Mechanical Tube
Revenue from External Customer [Line Items]
Net sales	367,730	445,453	395,289
Safety & Infrastructure \| Other Safety & Infrastructure products
Revenue from External Customer [Line Items]
Net sales	$ 475,982	$ 454,741	$ 302,863

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) - employee	12 Months Ended
SEGMENT INFORMATION - Narrative (Details) - employee	Sep. 30, 2023	Sep. 30, 2022	Jul. 14, 2020
Segment Reporting Information [Line Items]
Employees represented by a union under a collective bargaining agreement (approximately) (%)	18%
Number of employees represented by a union under a collective bargaining agreement			350
Accounts Receivable Benchmark \| Customer Concentration Risk \| Sonepar USA
Segment Reporting Information [Line Items]
Concentration risk, percentage	14%
Accounts Receivable Benchmark \| Customer Concentration Risk \| CED National
Segment Reporting Information [Line Items]
Concentration risk, percentage	11%	10%

SCHEDULE I - CONDENSED FINANC_2

SCHEDULE I - CONDENSED FINANCIAL INFORMATION - Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Assets
Total Assets	$ 2,935,009	$ 2,598,996	$ 2,210,099
Liabilities and Equity
Total Liabilities	1,466,890	1,349,209
Equity:
Common stock, $0.01 par value, 1,000,000,000 shares authorized, 37,317,893 and 41,351,350 shares issued and outstanding, respectively	374	415
Treasury stock, held at cost, 0 and 260,900 shares, respectively	0	(2,580)
Additional paid-in capital	506,783	500,117
Retained earnings	994,902	801,981
Accumulated other comprehensive loss	(33,940)	(50,146)
Total Equity	1,468,119	1,249,787	$ 864,736	$ 378,410
Total Liabilities and Equity	2,935,009	2,598,996
Parent Company
Assets
Investment in subsidiary	1,468,119	1,249,787
Total Assets	1,468,119	1,249,787
Liabilities and Equity
Total Liabilities	0	0
Equity:
Common stock, $0.01 par value, 1,000,000,000 shares authorized, 37,317,893 and 41,351,350 shares issued and outstanding, respectively	374	415
Treasury stock, held at cost, 0 and 260,900 shares, respectively	0	(2,580)
Additional paid-in capital	506,783	500,117
Retained earnings	994,902	801,981
Accumulated other comprehensive loss	(33,940)	(50,146)
Total Equity	1,468,119	1,249,787
Total Liabilities and Equity	$ 1,468,119	$ 1,249,787

SCHEDULE I - CONDENSED FINANC_3

SCHEDULE I - CONDENSED FINANCIAL INFORMATION - Balance Sheets Additional Information (Details) - $ / shares	Sep. 30, 2023	Sep. 30, 2022
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	37,317,893	41,351,350
Common stock, shares outstanding (in shares)	37,317,893	41,351,350
Treasury stock (in shares)	0	260,900
Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	37,317,893	41,351,350
Common stock, shares outstanding (in shares)	37,317,893	41,351,350
Treasury stock (in shares)	0	260,900

SCHEDULE I - CONDENSED FINANC_4

SCHEDULE I - CONDENSED FINANCIAL INFORMATION - Condensed Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Condensed Income Statements, Captions [Line Items]
Net income	$ 689,899	$ 913,434	$ 587,857
Other comprehensive (loss) income of subsidiary, net of tax	16,206	(21,420)	13,828
Comprehensive income	706,105	892,014	601,685
Parent Company
Condensed Income Statements, Captions [Line Items]
Net income	689,899	913,434	587,857
Other comprehensive (loss) income of subsidiary, net of tax	16,206	(21,420)	13,828
Comprehensive income	$ 706,105	$ 892,014	$ 601,685

SCHEDULE I - CONDENSED FINANC_5

SCHEDULE I - CONDENSED FINANCIAL INFORMATION - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Cash Flows from Operating Activities:
Net cash provided by operating activities	$ 807,634	$ 786,835	$ 572,902
Cash Flows from Investing Activities:
Net cash used for investing activities	(302,150)	(442,802)	(97,961)
Cash Flows from Financing Activities:
Repurchase of common shares	(491,033)	(500,161)	(135,066)
Net cash used for financing activities	(506,781)	(524,206)	(184,456)
Increase (decrease) in cash and cash equivalents	(637)	(187,538)	291,818
Cash and cash equivalents:
Cash and cash equivalents at beginning of period	388,751
Cash and cash equivalents at end of period	388,114	388,751
Parent Company
Cash Flows from Operating Activities:
Net cash provided by operating activities	0	0	0
Cash Flows from Investing Activities:
Distribution received from subsidiary	491,033	500,161	135,066
Distribution paid to subsidiary	14,428	24,045	(2,660)
Net cash used for investing activities	505,461	524,206	132,406
Cash Flows from Financing Activities:
Issuance of common stock, net of taxes withheld	(14,428)	(24,045)	2,660
Repurchase of common shares	(491,033)	(500,161)
Net cash used for financing activities	(505,461)	(524,206)	(132,406)
Increase (decrease) in cash and cash equivalents	0	0	0
Cash and cash equivalents:
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	$ 0	$ 0	$ 0

SCHEDULE I - CONDENSED FINANC_6

SCHEDULE I - CONDENSED FINANCIAL INFORMATION - Narrative (Details) - USD ($) $ in Thousands, shares in Millions			12 Months Ended
	Apr. 09, 2014	Mar. 06, 2014	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Dec. 22, 2010
Condensed Financial Statements, Captions [Line Items]
Payment to redeem shares	$ 250,000
Parent Company
Condensed Financial Statements, Captions [Line Items]
Distribution received from subsidiary			$ 491,033	$ 500,161	$ 135,066
Common Stock
Condensed Financial Statements, Captions [Line Items]
Non-binding letter of intent to acquire common stock (in shares)		40.3
Expense related to share redemption	$ 2,000
Atkore International \| CD&R
Condensed Financial Statements, Captions [Line Items]
Preferred stock, percentage of outstanding capital stock (on an as-converted basis) (%)						51%
Common stock, percentage of outstanding capital stock (%)						49%

SCHEDULE II - VALUATION AND Q_2

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Accounts Receivable Allowance for Current and Expected Credit Losses:
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ (2,544)	$ (2,510)	$ (3,167)
Additional (Charges)/Benefit to Income	(770)	(1,276)	(339)
Write offs and Other	(1,865)	1,242	996
Balance at End of Year	(5,179)	(2,544)	(2,510)
Deferred Tax Valuation Allowance:
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	(13,415)	(11,523)	(10,203)
Additional (Charges)/Benefit to Income	(44)	(5,265)	(2,190)
Write offs and Other	(5,620)	3,373	870
Balance at End of Year	$ (19,079)	$ (13,415)	$ (11,523)