Kaiser Aluminum (KALU) 10-Q6 May 212021 Q1 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2021	May 03, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-09447
Entity Registrant Name	KAISER ALUMINUM CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3030279
Entity Address, Address Line One	27422 Portola Parkway
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Foothill Ranch
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92610-2831
City Area Code	949
Local Phone Number	614-1740
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
Entity Shell Company	false
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	KALU
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		15,847,938
Entity Central Index Key	0000811596
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 128	$ 780.3
Receivables:
Trade receivables, net	305.8	112.8
Other	31.5	11.6
Contract assets	44.4	36.1
Inventories	385.3	152
Prepaid expenses and other current assets	35.8	28.6
Total current assets	930.8	1,121.4
Property, plant and equipment, net	1,006.6	627.2
Operating lease assets	38.9	26.5
Intangible assets, net	82.5	26.7
Goodwill	46.2	18.8
Other assets	47.8	44.1
Total	2,152.8	1,864.7
Current liabilities:
Accounts payable	259.6	86.1
Accrued salaries, wages and related expenses	31.9	30.8
Other accrued liabilities	58.9	41.4
Total current liabilities	350.4	158.3
Long-term portion of operating lease liabilities	34.1	25.6
Pension and other postretirement benefits	85	1.3
Net liabilities of Salaried VEBA	17.4	17.8
Deferred tax liabilities	15.9	13.9
Long-term liabilities	76.3	77.3
Long-term debt	838.7	838.1
Total liabilities	1,417.8	1,132.3
Commitments and contingencies
Stockholders’ equity:
Preferred stock, 5,000,000 shares authorized at both March 31, 2021 and December 31, 2020; no shares were issued and outstanding at March 31, 2021 and December 31, 2020
Common stock, par value $0.01, 90,000,000 shares authorized at both March 31, 2021 and December 31, 2020; 22,683,224 shares issued and 15,847,938 shares outstanding at March 31, 2021; 22,647,455 shares issued and 15,812,169 shares outstanding at December 31, 2020	0.2	0.2
Additional paid in capital	1,069.3	1,068.6
Retained earnings	151	158.2
Treasury stock, at cost, 6,835,286 shares at both March 31, 2021 and December 31, 2020	(475.9)	(475.9)
Accumulated other comprehensive loss	(9.6)	(18.7)
Total stockholders’ equity	735	732.4
Total	$ 2,152.8	$ 1,864.7

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common Stock, shares issued	22,683,224	22,647,455
Common stock, shares outstanding	15,847,938	15,812,169
Treasury stock, shares	6,835,286	6,835,286

STATEMENTS OF CONSOLIDATED INCO

STATEMENTS OF CONSOLIDATED INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Net sales	$ 324	$ 369.3
Costs and expenses:
Cost of products sold, excluding depreciation and amortization and other items	262.5	286.6
Depreciation and amortization	13.5	13.2
Selling, general, administrative, research and development	31.8	23.9
Restructuring benefit	(0.7)
Total costs and expenses	307.1	323.7
Operating income	16.9	45.6
Other expense:
Interest expense	(12.3)	(6.1)
Other expense, net – Note 11	(0.4)	(0.8)
Income before income taxes	4.2	38.7
Income tax benefit (provision)	0.3	(9.6)
Net income	$ 4.5	$ 29.1
Net income per common share:
Basic	$ 0.28	$ 1.83
Diluted	$ 0.28	$ 1.81
Weighted-average number of common shares outstanding (in thousands):
Basic	15,805	15,838
Diluted	15,987	16,008

STATEMENTS OF CONSOLIDATED COMP

STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 4.5	$ 29.1
Other comprehensive income (loss), net of tax
Defined benefit pension plan and Salaried VEBA	0.7	1.1
Available for sale securities		(0.2)
Cash flow hedges	8.5	(15.9)
Fair value hedges		(0.5)
Foreign currency translation	(0.1)
Other comprehensive income (loss), net of tax	9.1	(15.5)
Comprehensive income	$ 13.6	$ 13.6

STATEMENTS OF CONSOLIDATED STOC

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions		Total	Common Stock		Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2019		$ 733.9	$ 0.2		$ 1,062.9	$ 172.8	$ (463.4)	$ (38.6)
Beginning balance (shares) at Dec. 31, 2019			15,868,304
Stockholders' Equity [Roll Forward]
Net income		29.1				29.1
Other comprehensive income (loss), net of tax		(15.5)						(15.5)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			119,598
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(4.3)			(4.3)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(45,545)
Repurchase of common stock	[1]	(12.5)					(12.5)
Repurchase of common stock (shares)	[1]		(152,763)
Cash dividends declared	[2]	(11.3)				(11.3)
Amortization of unearned equity compensation		1.7			1.7
Ending balance at Mar. 31, 2020		721.1	$ 0.2		1,060.3	190.6	(475.9)	(54.1)
Ending balance (shares) at Mar. 31, 2020			15,789,594
Beginning balance at Dec. 31, 2020		$ 732.4	$ 0.2		1,068.6	158.2	(475.9)	(18.7)
Beginning balance (shares) at Dec. 31, 2020		15,812,169	15,812,169	[3],[4]
Stockholders' Equity [Roll Forward]
Net income		$ 4.5				4.5
Other comprehensive income (loss), net of tax		9.1						9.1
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[3],[4]		56,394
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(2.4)			(2.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)	[3],[4]		(20,625)
Repurchase of common stock (shares)			0
Cash dividends declared	[5]	(11.7)				(11.7)
Amortization of unearned equity compensation		3.1			3.1
Ending balance at Mar. 31, 2021		$ 735	$ 0.2		$ 1,069.3	$ 151	$ (475.9)	$ (9.6)
Ending balance (shares) at Mar. 31, 2021		15,847,938	15,847,938	[3],[4]

[1]	Weighted-average repurchase price (dollars per share) for the quarter ended March 31, 2020 was $81.94.
[2]	Dividends declared per common share was $0.67
[3]	At March 31, 2021, 232,320
[4]	There were no repurchases of common stock during the quarter ended March 31, 2021. At March 31, 2021, $93.1
[5]	Dividends declared per common share was $0.72 for the quarter ended March 31, 2021.

STATEMENTS OF CONSOLIDATED ST_2

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Shares available for awards (shares)	232,320
Weighted average repurchase price (in dollars per share)		$ 81.94
Repurchase amount remaining	$ 93.1
Cash dividends declared (in dollars per share)	$ 0.72	$ 0.67
Common Stock
Repurchases of common stock	0	152,763	[1]

[1]	Weighted-average repurchase price (dollars per share) for the quarter ended March 31, 2020 was $81.94.

STATEMENTS OF CONSOLIDATED CASH

STATEMENTS OF CONSOLIDATED CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 4.5	$ 29.1
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment	12.8	12.5
Amortization of definite-lived intangible assets	0.7	0.7
Amortization of debt premium and debt issuance costs	0.7	0.3
Deferred income taxes	(0.9)	14.8
Non-cash equity compensation	3.1	1.7
Gain on disposition of short-term investments		(0.5)
Loss on disposition of property, plant and equipment		0.2
Changes in operating assets and liabilities, net of effects of acquisition:
Trade and other receivables	(31.7)	(12.6)
Contract assets	(8.3)	7.5
Inventories	(24.3)	(17)
Prepaid expenses and other current assets	(0.4)	(2.6)
Accounts payable	33	21.7
Accrued liabilities	4.2	(2.4)
Annual variable cash contributions to Salaried VEBA	(1.7)	(2.9)
Long-term assets and liabilities, net	(3.1)	1.9
Net cash (used in) provided by operating activities	(11.4)	52.4
Cash flows from investing activities:
Capital expenditures	(9.1)	(21.1)
Cash payment for acquisition of Warrick Rolling Mill	(617.5)
Purchase of short-term investments		(39.1)
Proceeds from disposition of short-term investments		78.8
Net cash (used in) provided by investing activities	(626.6)	18.6
Cash flows from financing activities:
Repayment of finance lease	(0.4)	(0.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares	(2.4)	(4.3)
Repurchase of common stock		(12.5)
Cash dividends and dividend equivalents paid	(11.7)	(11.3)
Net cash used in financing activities	(14.5)	(28.5)
Net (decrease) increase in cash, cash equivalents and restricted cash during the period	(652.5)	42.5
Cash, cash equivalents and restricted cash at beginning of period	794.3	278.6
Cash, cash equivalents and restricted cash at end of period	$ 141.8	$ 321.1

Basis of Presentation and Recen

Basis of Presentation and Recent Accounting Pronouncements	3 Months Ended
Basis of Presentation and Recent Accounting Pronouncements	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Recent Accounting Pronouncements	1. Basis of Presentation and Recent Accounting Pronouncements This Quarterly Report on Form 10-Q (this “Report”) should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. Unless the context otherwise requires, references in these notes to interim consolidated financial statements - unaudited to “Kaiser Aluminum Corporation,” “we,” “us,” “our,” “the Company” and “our Company” refer collectively to Kaiser Aluminum Corporation and its subsidiaries. Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with United States generally accepted accounting principles (“GAAP”) and the rules and regulations of the Securities and Exchange Commission (“SEC”) applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management’s opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2021 fiscal year. The financial information as of December 31, 2020 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2020. We have reclassified certain amounts in prior-period financial statements to conform to the current period's presentation. On the Consolidated Balance Sheets, prior period presentation of the Canadian pension plan in Long-term liabilities is now reflected in Pension and other postretirement benefits. On the Statements of Consolidated Cash Flows, prior period presentation of Other non-cash changes in assets and liabilities is now reflected in Changes in operating assets and liabilities within the following categories: (i) Prepaid expenses and other current assets; (ii) Accrued liabilities; and (iii) Long-term assets and liabilities, net. Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations. Supply Chain Financing . Upon our acquisition of the Warrick Rolling Mill (as defined in Note 4 below), we became party to several supply chain financing arrangements, in which we may sell certain of our customers’ trade accounts receivable to such customers’ financial institutions without recourse. We sell our undivided interests in certain of these receivables at our discretion when we determine that the cost of these arrangements is less than the cost of servicing our receivables with existing debt. Under the terms of the agreements, we retain no rights or interest, have no obligations with respect to the sold receivables and do not service the receivables after the sale. As such, these transactions are being accounted for as a sale. Discount fees related to the sale of trade accounts receivable under supply chain financing arrangements will be included in Other expense, net. There were no such discount fees recognized during the quarter ended March 31, 2021. Adoption of New Accounting Pronouncements In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2019-12, Simplifying the Accounting for Income Taxes Accounting Pronouncements Issued But Not Yet Adopted In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	3 Months Ended
Supplemental Balance Sheet Information	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Supplemental Balance Sheet Information	2. Supplemental Balance Sheet Information As of March 31, 2021 As of December 31, 2020 (In millions of dollars) Trade Receivables, Net Billed trade receivables $ 306.7 $ 113.6 Allowance for doubtful receivables (0.9 ) (0.8 ) Trade receivables, net $ 305.8 $ 112.8 Inventories 1 Finished products $ 83.0 $ 37.2 Work-in-process 178.5 46.0 Raw materials 117.7 62.3 Operating supplies 6.1 6.5 Total $ 385.3 $ 152.0 Property, Plant and Equipment, Net Land and improvements $ 26.9 $ 21.5 Buildings and leasehold improvements 176.0 117.2 Machinery and equipment 1,144.7 847.4 Construction in progress 2 68.4 37.8 Property, plant and equipment, gross 1,416.0 1,023.9 Accumulated depreciation and amortization (411.1 ) (398.4 ) Assets held for sale 1.7 1.7 Property, plant and equipment, net $ 1,006.6 $ 627.2 Other Accrued Liabilities Uncleared cash disbursements $ 7.0 $ 2.1 Accrued income taxes and other taxes payable 10.4 5.2 Accrued annual contribution to Salaried VEBA — 1.7 Accrued interest 11.5 11.6 Short-term environmental accrual – Note 8 4.0 3.7 Other – Note 3 and Note 6 26.0 17.1 Total $ 58.9 $ 41.4 Long-Term Liabilities Workers' compensation accrual $ 30.2 $ 30.6 Long-term environmental accrual – Note 8 14.0 15.1 Other long-term liabilities 32.1 31.6 Total $ 76.3 $ 77.3 1 At March 31, 2021 and December 31, 2020 the current cost of our inventory exceeded its stated last-in, first-out (“LIFO”) value by $24.0 million and $8.4 million 2 Based on market conditions during the quarter ended March 31, 2021, $20.1 million within Construction in progress as of March 31, 2021 related to temporarily idled projects, all of which are expected to resume at a future date.

Leases

Leases	3 Months Ended
Leases	Mar. 31, 2021
Leases [Abstract]
Leases	3. Leases We determine whether an agreement is a lease at inception. We have operating and finance leases for equipment and real estate that primarily have fixed lease payments. Our leases have remaining lease terms of approximately one to 60 years, some of which may include options to extend the lease for up to 60 years and some of which may include options to terminate the lease within one year. For purposes of calculating lease liabilities, these options are included within the lease term when it has become reasonably certain that we will exercise such options . Short-term leases with an initial term of 12 months or less are not recorded on our Consolidated Balance Sheets. As most of our leases do not provide an implicit rate, we use information available at the lease commencement date in determining an incremental borrowing rate when calculating our right-of-use lease assets and liabilities. In determining the inputs to the incremental borrowing rate calculation, we make judgments about the value of the leased asset, our credit rating and the lease term, including the probability of our exercising options to extend or terminate the underlying lease. Additionally, we make judgments around contractual asset substitution rights in determining whether a contract contains a lease. We have lease agreements with lease and non-lease components, which are generally accounted for separately. These non-lease components include items such as common area maintenance, taxes and insurance for our real estate leases, as well as maintenance charges related to our equipment leases. We have, however, applied the practical expedient within ASU 2016-02 to not separate lease and non-lease components to our embedded supply system equipment leases and have therefore accounted for both lease and non‑lease components in determining the lease assets and liabilities. Many of our equipment leases contain clauses that require us to return the equipment with certain functionality intact. We account for these costs as residual value guarantees when the guarantee becomes probable of being owed. Our lease agreements do not contain any material restrictive covenants. The following table presents lease terms and discount rates as of March 31, 2021: Finance Leases Operating Leases Weighted-average lease term (in years) 24.0 7.5 Weighted-average discount rate 3.5 % 4.2 % The following table summarizes the classification of lease assets and lease liabilities on our Consolidated Balance Sheets (in millions of dollars): Leases Classification As of March 31, 2021 As of December 31, 2020 Assets Operating lease assets Operating lease assets $ 38.9 $ 26.5 Finance lease assets Property, plant and equipment, net 9.6 8.1 Total lease assets $ 48.5 $ 34.6 Liabilities Current: Operating lease liabilities Other accrued liabilities $ 8.1 $ 4.4 Finance lease liabilities Other accrued liabilities 2.0 1.9 Non-current: Operating lease liabilities Long-term portion of operating lease liabilities 34.1 25.6 Finance lease liabilities Long-term liabilities 7.6 6.2 Total lease liabilities $ 51.8 $ 38.1 The following table summarizes the components of lease cost on our Statements of Consolidated Income (in millions of dollars): Quarter Ended March 31, 2021 2020 Operating lease cost $ 2.0 $ 1.8 Short-term lease cost 0.2 0.3 Finance lease cost: Amortization of leased assets 0.5 0.4 Interest on lease liabilities 0.1 0.1 Total lease cost $ 2.8 $ 2.6 The following table presents the maturity of our lease liabilities as of March 31, 2021 (in millions of dollars): Maturity of Lease Liabilities Finance Leases Operating Leases Remainder of 2021 $ 1.8 $ 7.3 2022 2.1 8.9 2023 1.8 7.5 2024 1.3 6.7 2025 1.1 3.6 Thereafter 6.6 17.0 Total minimum lease payments $ 14.7 $ 51.0 Less: interest (5.1 ) (8.8 ) Present value $ 9.6 $ 42.2

Business Combinations, Goodwill

Business Combinations, Goodwill and Intangible Assets	3 Months Ended
Business Combinations, Goodwill and Intangible Assets	Mar. 31, 2021
Business Combinations And Goodwill Disclosure [Abstract]
Business Combinations, Goodwill and Intangible Assets	4. Business Combinations, Goodwill and Intangible Assets Warrick Rolling Mill Acquisition . On March 31, 2021, we acquired Alcoa Warrick LLC and certain assets comprising the aluminum casting and rolling mill facility located in Warrick County, Indiana (collectively, the “Warrick Rolling Mill”) for a purchase price of $670.0 million. The Warrick Rolling Mill is a leading producer of can stock for the beverage and food packaging industry in North America. The transaction provides us with non-cyclical end market diversification and re-entry into the packaging end market. Acquisition-related costs incurred and expensed during the quarter ended March 31, 2021 were $11.0 million, primarily related to legal and consulting fees and included within Selling, general, administrative, research and development (“SG&A and R& D”) . The preliminary purchase consideration to allocate was determined as follows (in millions of dollars): Contract purchase price $ 670.0 Preliminary working capital adjustment 31.0 Initial outstanding indebtedness – Other postretirement benefits liabilities (83.5 ) Cash paid at acquisition close on March 31, 2021 617.5 Estimate of post-close adjustments (12.7 ) Total preliminary purchase consideration to allocate $ 604.8 The preliminary purchase consideration to allocate is subject to customary post-closing adjustments, estimates of which are included in the table above. We prepared an initial allocation of the purchase consideration as of the acquisition date based on our understanding of the fair value of the acquired assets and assumed liabilities. As we continue to obtain additional information supporting the final valuation of inventories, property, plant and equipment, intangible assets and long-term liabilities, we will refine the estimates of fair value and may revise our allocation of the purchase consideration. We expect to finalize the valuation of the assets and liabilities, as well as the post-closing adjustments as soon as practicable, but in any event no later than one year from the acquisition date. The following table summarizes the preliminary fair values of assets acquired and liabilities assumed at the acquisition date (in millions of dollars): Trade receivables $ 162.4 Other receivables 6.2 Inventories, including step up 209.0 Property, plant and equipment 385.4 Operating lease assets 12.3 Intangible assets 56.5 Goodwill 27.4 Accounts payable (143.0 ) Accrued salaries, wages and related expenses (5.9 ) Other accrued liabilities (11.5 ) Long-term portion of operating lease liabilities (8.7 ) Pension and other postretirement benefits (83.7 ) Long-term liabilities (1.6 ) Preliminary allocated purchase consideration $ 604.8 Intangible Assets. The following table presents the components of acquired intangible assets and their estimated useful lives as of the date of acquisition (in millions of dollars): Useful Life (in years) Fair Value Favorable lease contract 120 $ 7.0 Favorable commodity contracts 2 11.0 Customer relationships 12 38.5 Total $ 56.5 Goodwill. Goodwill related to the Warrick Rolling Mill acquisition is primarily attributable to the assembled workforce and is expected to be deductible for income tax purposes. The following table presents the changes to goodwill during the quarter ended March 31, 2021 (in millions of dollars): Gross Carrying Value Accumulated Impairment Loss Net Carrying Value Balance as of December 31, 2020 $ 37.2 $ (18.4 ) $ 18.8 Warrick Rolling Mill acquisition 27.4 — 27.4 Balance as of March 31, 2021 $ 64.6 $ (18.4 ) $ 46.2 Results of the Warrick Rolling Mill. The acquisition of the Warrick Rolling Mill was completed after the close of business on March 31, 2021. As such, there are no amounts to be included in our Statements of Consolidated Income. Certain Unaudited Pro Forma Information. The following unaudited pro forma financial information presents what our results would have been had the Warrick Rolling Mill been acquired on January 1, 2020. The unaudited pro forma information includes adjustments and consequential tax effects related to: (i) amortization and depreciation for intangible assets and property, plant and equipment acquired; (ii) the effects of certain reclassifications and conforming accounting policies; and (iii) acquisition-related transaction costs. The unaudited pro forma information presented below is for informational purposes only and is not necessarily indicative of our consolidated results of operations of the consolidated business had the acquisition occurred at the beginning of fiscal year 2020 or of the results of our future operations of the consolidated business. Quarter Ended March 31, 2021 2020 Net sales $ 635.9 $ 636.1 Net income $ 9.9 $ 3.5 The Warrick Rolling Mill has historically purchased aluminum and electrical power from Alcoa Corporation's smelter in Warrick County, Indiana. Alcoa Corporation’s Warrick smelter historically sold the aluminum to the Warrick Rolling Mill at smelter cost and electrical power from Alcoa Corporation's power plant in Warrick County, Indiana at negotiated prices between the parties. As part of the acquisition of the Warrick Rolling Mill, we negotiated pricing for aluminum and electrical power with Alcoa Corporation at alternative rates which more closely align with market pricing. The table above does not reflect the cost of aluminum and electrical power under these negotiated rates.

Employee Benefits

Employee Benefits	3 Months Ended
Employee Benefits	Mar. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Employee Benefits	5. Employee Benefits Short-Term Incentive Plans (“STI Plans”). We have annual short-term incentive compensation plans for senior management and certain other employees payable at our election in cash, shares of common stock or a combination of cash and shares of common stock. Amounts earned under STI Plans are based on our adjusted earnings before interest, taxes, depreciation and amortization (“Adjusted EBITDA”), modified for certain safety, quality, delivery, cost and individual performance factors. The Adjusted EBITDA targets are determined based on the return on adjusted net assets. Most of our production facilities have similar programs for both hourly and salaried employees. As of March 31, 2021, we had a liability of $2.7 million recorded within Accrued salaries, wages and related expenses for estimated probable future payments relating to the three month performance period of our 2021 STI Plan. Pension and Similar Benefit Plans. We provide contributions to: (i) defined contribution 401(k) savings plans for salaried employees and certain hourly employees; (ii) a non-qualified, unfunded, unsecured plan of deferred compensation (see “ ” below); (iii) multi-employer pension plans sponsored by the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union, AFL-CIO, CLC, the International Association of Machinists and certain other unions at certain of our production facilities; and (iv) a defined benefit pension plan for salaried employees at our London, Ontario (Canada) facility. Deferred Compensation Plan . We have a non-qualified, unfunded, unsecured plan of deferred compensation for certain employees who would otherwise suffer a loss of benefits under our defined contribution plan as a result of the limitations imposed by the Internal Revenue Code of 1986. Despite the plan being an unfunded plan, we make an annual contribution to a rabbi trust to fulfill future funding obligations as contemplated by the terms of the plan. The assets in the trust are held in various investment funds at certain registered investment companies and are accounted for as equity investments with changes in fair value recorded within Other expense, net (see Note 11). Assets of our deferred compensation plan are included in Other assets, classified within Level 2 of the fair value hierarchy and are measured and recorded at fair value based on their quoted market prices. The fair value of these assets at March 31, 2021 and December 31, 2020 was $9.5 million and $9.6 million, respectively. Offsetting liabilities relating to the deferred compensation plan are included in Other accrued liabilities and Long-term liabilities. Salaried VEBA Postretirement Obligation. Certain retirees who retired prior to 2004 and certain employees who were hired prior to February 2002 and have subsequently retired or will retire with the requisite age and service, along with their surviving spouses and eligible dependents, are eligible to participate in a voluntary employees’ beneficiary association (“VEBA”) that provides healthcare cost, medical cost and long-term care insurance cost reimbursement benefits (“Salaried VEBA”). We have an ongoing obligation with no express termination date to make annual variable cash contributions up to a maximum of $2.9 million to the Salaried VEBA. We paid $1.7 million with respect to 2020 during the quarter ended March 31, 2021. We account for the Salaried VEBA as a defined benefit plan in our financial statements. Warrick Rolling Mill Pension and Other Postretirement Benefits . In conjunction with the Warrick Rolling Mill acquisition, we assumed certain defined benefit pension obligations for certain union employees hired prior to January 1, 2020 and other postretirement benefit (“OPEB”) obligations relating to retiree medical and life insurance benefits for certain union employees hired prior to July 1, 2010, and were active union employees of the Warrick Rolling Mill on March 31, 2021 and we agreed to establish new plans with respect to each. Pension and OPEB liabilities and expenses are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated liability, the expected long-term rate of return on plan assets and several assumptions relating to the employee workforce (salary increases, health care cost trend rates, retirement age and mortality). The following data presents the key assumptions used and the amounts reflected in our consolidated financial statements with respect to the Warrick Rolling Mill’s pension plan and OPEB. We used a March 31 measurement date for both of the plans. The following table presents the assumptions used to determine the Warrick Rolling Mill pension and OPEB obligations: Warrick Pension Plan Warrick OPEB As of March 31, 2021 As of March 31, 2021 Discount rate 3.24 % 2.97 % Expected long-term return on plan assets 7.00 % N/A Trend rate (initial) N/A 5.40 % Trend rate (ultimate) N/A 4.00 % Years to reach ultimate trend N/A 14 Rate of compensation increase 2.50 % — The accumulated benefit obligation at March 31, 2021 for the Warrick Rolling Mill’s pension plan and OPEB was $6.7 million and $78.0 million, respectively, of which $1.0 million was recorded within Other accrued liabilities. Our expected minimum contributions to the Warrick Rolling Mill pension plan and OPEB in 2021 is $0.1 million and $0.7 million, respectively. The following table presents the minimum net benefits expected to be paid (in millions of dollars): Year Ended December 31, 2021 2022 2023 2024 2025 2026-2030 Warrick pension plan benefit payments $ 0.1 $ 0.1 $ 0.2 $ 0.3 $ 0.5 $ 4.4 Warrick OPEB plan benefit payments 0.7 1.6 2.3 3.0 3.7 27.2 Total net benefits $ 0.8 $ 1.7 $ 2.5 $ 3.3 $ 4.2 $ 31.6 The following table presents the total expense related to all postretirement benefit plans (in millions of dollars): Quarter Ended March 31, 2021 2020 Defined contribution plans 1 $ 3.4 $ 3.9 Deferred compensation plan 2 — (0.4 ) Multiemployer pension plans 1 1.1 1.3 Net periodic postretirement benefit cost relating to Salaried VEBA 2 0.6 1.2 Total $ 5.1 $ 6.0 1 2 Components of Net Periodic Postretirement Benefit Cost. Our results of operations included the following impacts associated with our Canadian pension plan and the Salaried VEBA: (i) a charge for service rendered by employees; (ii) a charge for accretion of interest; (iii) a benefit for the expected return on plan assets; (iv) amortization of prior service costs associated with plan amendments; and (v) amortization of net actuarial differences. Net periodic benefit cost related to our Canadian pension plan was not material for the quarter ended March 31, 2021 . The following table presents the components of Net periodic postretirement benefit cost relating to Salaried VEBA (in millions of dollars): Quarter Ended March 31, 2021 2020 Salaried VEBA 1 Interest cost $ 0.4 $ 0.6 Expected return on plan assets (0.8 ) (0.7 ) Amortization of prior service cost 2 0.9 1.2 Amortization of net actuarial loss 0.1 0.1 Total net periodic postretirement benefit cost relating to Salaried VEBA $ 0.6 $ 1.2 1 2

Derivatives, Hedging Programs a

Derivatives, Hedging Programs and Other Financial Instruments	3 Months Ended
	Mar. 31, 2021
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivatives, Hedging Programs and Other Financial Instruments	6. Derivatives, Hedging Programs and Other Financial Instruments Overview. In conducting our business, we enter into derivative transactions, including forward contracts and options, to limit our exposure to: (i) metal price risk related to our sale of fabricated aluminum products and the purchase of metal used as raw material for our fabrication operations; (ii) energy price risk relating to fluctuating prices of natural gas and electricity used in our production processes; and (iii) foreign currency requirements with respect to cash commitments for equipment purchases denominated in foreign currency. We do not use derivative financial instruments for trading or other speculative purposes. Hedging transactions are executed centrally on behalf of all of our operations to minimize transaction costs, monitor consolidated net exposures and allow for increased responsiveness to changes in market factors. Our derivative activities are overseen by a committee (“Hedging Committee”), which is composed of our chief executive officer, chief financial officer, chief accounting officer, vice president of treasury, risk and procurement and other officers and employees selected by the chief executive officer. We are exposed to counterparty credit risk on all of our derivative instruments, which we manage by monitoring the credit quality of our counterparties and allocating our hedging positions among multiple counterparties to limit exposure to any single entity. Our counterparties are major investment grade financial institutions or trading companies. Hedging transactions are governed by negotiated reciprocal credit lines, which generally require collateral to be posted above specified credit thresholds. We believe the risk of loss is remote and contained due to counterparty credit quality, our diversification practice and collateral requirements. In a majority of our hedging counterparty agreements, our counterparty offers us a credit line that adjusts up or down, depending on our liquidity. Below specified liquidity thresholds, we may have to post collateral if the fair value of our net liability with such counterparty exceeds our reduced credit line. We manage this risk by allocating hedging transactions among multiple counterparties, using options as part of our hedging activities or both. The aggregate fair value of our derivative instruments that were in a net liability position was $0.2 million Additionally, our firm-price customer sales commitments create incremental customer credit risk related to metal price movements. Under certain circumstances, we mitigate this risk by periodically requiring cash collateral from them, which we classify as deferred revenue and include as a component of Other accrued liabilities. We had no cash collateral posted from our customers at both March 31, 2021 and December 31, 2020. For more information about concentration risks concerning customers and suppliers, see Note 15. Cash Flow Hedges We designate forward swap contracts for aluminum, energy and, from time-to-time, zinc and copper (“Alloying Metals”), used in our fabrication operations as cash flow hedges. Unrealized gains and losses associated with our cash flow hedges are deferred in Other comprehensive income (loss), net of tax, and reclassified to COGS when such hedges settle or when it is probable that the original forecasted transactions will not occur by the end of the originally specified time period. See Note 9 for the total amount of gain or loss on derivative instruments designated and qualifying as cash flow hedging instruments and fair value hedging instruments that was reported in Accumulated other comprehensive loss (“AOCI”), as well as the related reclassifications into earnings and tax effects. Cumulative gains and losses related to cash flow hedges are reclassified out of AOCI and recorded within COGS when the associated hedged commodity purchases impact earnings. Aluminum Hedges . Our pricing of fabricated aluminum products is generally intended to lock in a conversion margin (representing the value added from the fabrication process(es)) and to pass through metal price fluctuations to our customers. For some of our higher value added products sold on a spot basis, the pass through of metal price movements can sometimes lag by as much as several months, with a favorable impact to us when metal prices decline and an adverse impact to us when metal prices increase. Additionally, in certain instances, we enter into firm-price arrangements with our customers for stipulated volumes to be delivered in the future. Because we generally purchase primary and secondary aluminum on a floating price basis, the lag in passing through metal price movements to customers on some of our higher value added products sold on a spot basis and the volume that we have committed to sell to our customers under a firm-price arrangement create metal price risk for us. We use third-party hedging instruments to limit exposure to metal price risk related to the metal pass through lag on some of our products and firm-price customer sales contracts. Alloying Metals Hedges . We are exposed to risk of fluctuating prices for Alloying Metals used as raw materials in our fabrication operations. We, from time to time, in the ordinary course of business, use third-party hedging instruments to mitigate our risk from price fluctuations in Alloying Metals. Energy Hedges . We are exposed to risk of fluctuating prices for natural gas and electricity. We, from time to time, in the ordinary course of business, enter into hedging transactions and/or physical delivery commitments with third parties to mitigate our risk from fluctuations in natural gas and electricity prices. The following table summarizes the volume of our derivative and/or physical delivery commitments with energy companies in place to cover our exposure to price fluctuations of our expected variable priced energy purchases as of March 31, 2021: Remainder of 2021 2022 2023 2024 2025 2026 Natural Gas 46% 50% 49% 45% 20% 20% Electricity 96% 76% 44% — — — Fair Value Hedges We are exposed to foreign currency exchange risk related to firm-price commitments for equipment purchases from foreign manufacturers. We, from time to time, in the ordinary course of business, use third-party hedging instruments to mitigate our exposure to currency exchange rate fluctuations on these purchases and designate such hedging instruments as fair value hedges. Gain or loss related to components excluded from the assessment of effectiveness from these fair value hedges is first recognized in AOCI and subsequently reclassified to Depreciation and amortization on a straight-line basis over the term of the hedge. Gain or loss on the hedged item (e.g., equipment purchase firm commitments) and the remaining gain or loss on the fair value hedge is recorded within Depreciation and amortization in the period that the gain or loss occurs. Any difference between the change in the fair value of the excluded component and amounts recognized in income on a straight-line basis over the term of the hedge is recognized in AOCI. Non-Designated Hedges of Operational Risks From time-to-time, we enter into commodity and foreign currency exchange contracts that are not designated as hedging instruments to mitigate certain short-term commodity and currency impacts, as identified. For derivative instruments that are not designated as hedging instruments, the gain or loss on these derivatives is recognized within COGS or Other expense, net, depending on whether it relates to commodity risk or foreign currency risk, respectively. Notional Amount of Derivative Contracts The following table summarizes our derivative positions at March 31, 2021: Aluminum Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 4/21 through 12/23 113.5 Fixed price sales contracts 4/21 through 11/21 0.9 Midwest premium swap contracts 1 4/21 through 12/23 69.1 Alloying Metals Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 4/21 through 12/22 9.1 Fixed price sales contracts 4/21 through 12/21 3.2 Natural Gas Maturity Period (month/year) Notional Amount of Contracts (mmbtu) Fixed price purchase contracts 4/21 through 12/24 6,060,000 Electricity Maturity Period (month/year) Notional Amount of Contracts (Mwh) Fixed price purchase contracts 4/21 through 12/22 417,030 1 Regional premiums represent the premium over the London Metal Exchange price for primary aluminum which is incurred on our purchases of primary aluminum. (Gain) Loss The following table summarizes the amount of (gain) loss included on our Statements of Consolidated Income associated with all derivative contracts (in millions of dollars): Quarter Ended March 31, Statements of Consolidated 2021 2020 Income Classification Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of hedges are recorded: Cash flow hedges $ 262.5 $ 286.6 Cost of products sold Fair value hedges n/a $ 13.2 Depreciation and amortization (Gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges: Aluminum $ (2.9 ) $ 5.7 Cost of products sold Alloying Metals (0.9 ) 0.6 Cost of products sold Natural gas — 0.5 Cost of products sold Electricity — 0.2 Cost of products sold Total (gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges $ (3.8 ) $ 7.0 Loss (gain) recognized in our Statements of Consolidated Income related to fair value hedges: Foreign exchange contracts $ — $ 0.2 Depreciation and amortization Hedged item — (0.2 ) Depreciation and amortization Excluded component amortized from AOCI — 0.2 Depreciation and amortization Total loss recognized in our Statements of Consolidated Income related to fair value hedges $ — $ 0.2 Gain recognized in our Statements of Consolidated Income related to non-designated hedges: Alloying Metals – Unrealized gain $ (0.3 ) $ — Cost of products sold Total gain recognized in our Statements of Consolidated Income related to non-designated hedges: $ (0.3 ) $ — Fair Values of Derivative Contracts The fair values of our derivative contracts are based upon trades in liquid markets. Valuation model inputs can be verified, and valuation techniques do not involve significant judgment. The fair values of such financial instruments are classified within Level 2 of the fair value hierarchy. All of our derivative contracts with counterparties are subject to enforceable master netting arrangements. We reflect the fair value of our derivative contracts on a gross basis on our Consolidated Balance Sheets. The following table presents the fair value of our derivative financial instruments (in millions of dollars): As of March 31, 2021 As of December 31, 2020 Assets Liabilities Net Amount Assets Liabilities Net Amount Cash Flow Hedges: Aluminum – Fixed price purchase contracts $ 8.9 $ (0.1 ) $ 8.8 $ 4.6 $ (0.1 ) $ 4.5 Fixed price sales contracts — (0.1 ) (0.1 ) — — — Midwest premium swap contracts 3.0 — 3.0 0.2 (1.2 ) (1.0 ) Natural gas – Fixed price purchase contracts 0.3 (1.1 ) (0.8 ) 0.2 (1.5 ) (1.3 ) Electricity – Fixed price purchase contracts 3.7 (1.7 ) 2.0 2.0 (2.5 ) (0.5 ) Total cash flow hedges 15.9 (3.0 ) 12.9 7.0 (5.3 ) 1.7 Non-Designated Hedges: Alloying Metals – Fixed price purchase contracts 4.2 (0.1 ) 4.1 3.9 — 3.9 Fixed price sales contracts — (1.2 ) (1.2 ) — (1.3 ) (1.3 ) Total non-designated hedges 4.2 (1.3 ) 2.9 3.9 (1.3 ) 2.6 Total $ 20.1 $ (4.3 ) $ 15.8 $ 10.9 $ (6.6 ) $ 4.3 The following table presents the total amounts of derivative assets and liabilities on our Consolidated Balance Sheets (in millions of dollars): As of March 31, 2021 As of December 31, 2020 Derivative assets: Prepaid expenses and other current assets $ 15.5 $ 8.4 Other assets 4.6 2.5 Total derivative assets $ 20.1 $ 10.9 Derivative liabilities: Other accrued liabilities $ (2.2 ) $ (3.8 ) Long-term liabilities (2.1 ) (2.8 ) Total derivative liabilities $ (4.3 ) $ (6.6 ) Fair Value of Other Financial Instruments All Other Financial Assets and Liabilities. We believe that the fair values of our accounts receivable, contract assets, accounts payable and accrued liabilities approximate their respective carrying values due to their short maturities and nominal credit risk.

Debt and Credit Facility

Debt and Credit Facility	3 Months Ended
Debt and Credit Facility	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt and Credit Facility	7. Debt and Credit Facility Senior Notes 6.50% Senior Notes. In April 2020 and May 2020, we issued $300.0 million and $50.0 million, respectively, aggregate principal amounts of our 6.50% unsecured senior notes due May 1, 2025 at 100% and 101%, respectively, of the principal amounts (“6.50% Senior Notes”). The unamortized amount of debt issuance costs relating to the 6.50% Senior Notes as of March 31, 2021 was $5.0 million . Interest expense, including amortization of debt issuance costs and debt premium , relating to the 6.50% Senior Notes was $6.0 million for the quarter ended March 31, 2021 . The effective interest rate of the 6.50% Senior Notes is approximately 6.8% per annum, taking into account the amortization of premium and debt issuance costs. The fair value of the outstanding 6.50% Senior Notes, which are Level 1 liabilities calculated based on pricing from trades around the balance sheet date, was approximately $371.3 million and $376.8 million at March 31, 2021 and December 31, 2020 , respectively. 4.625% Senior Notes. In November 2019, we issued $500.0 million principal amount of 4.625% unsecured senior notes due March 1, 2028 at 100% of the principal amount (“4.625% Senior Notes”). The unamortized amount of debt issuance costs as of March 31, 2021 was $6.3 million. Interest expense, including amortization of debt issuance costs, relating to the 4.625% Senior Notes was $6.0 million for both quarters ended March 31, 2021 and March 31, 2020. The effective interest rate of the 4.625% Senior Notes was approximately 4.8% per annum, taking into account the amortization of debt issuance costs. The fair value of the outstanding 4.625% Senior Notes, which are Level 1 liabilities, was approximately $511.7 million and $521.3 million at March 31, 2021 and December 31, 2020, respectively. The amount of interest expense capitalized as construction in progress was $0.1 million and $0.3 million during the quarters ended March 31, 2021 and March 31, 2020, respectively. Revolving Credit Facility Our credit agreement with Wells Fargo Bank, National Association, as administrative agent, and the other financial institutions party thereto (“Revolving Credit Facility”) provides us with a $375.0 million funding commitment through October 2024. The following table summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of March 31, 2021 (in millions of dollars except for borrowing rate): Revolving Credit Facility borrowing commitment $ 375.0 Borrowing base availability $ 375.0 Less: Outstanding borrowings under Revolving Credit Facility — Less: Outstanding letters of credit under Revolving Credit Facility (7.8 ) Remaining borrowing availability $ 367.2 Borrowing rate (if applicable) 1 3.50 % 1

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Commitments. We have a variety of financial commitments, including purchase agreements, forward foreign exchange and forward sales contracts, indebtedness and letters of credit (see Note 6 and Note 7). Environmental Contingencies. We are subject to a number of environmental laws and regulations, to potential fines or penalties assessed for alleged breaches of such laws and regulations and to potential claims based upon such laws and regulations. We are also subject to legacy environmental contingencies related to activities that occurred at operating facilities prior to July 6, 2006, which represent the majority of our environmental accruals. The status of these environmental contingencies are discussed below. We have established procedures for regularly evaluating environmental loss contingencies. Our environmental accruals represent our undiscounted estimate of costs reasonably expected to be incurred based on presently enacted laws and regulations, currently available facts, existing requirements, existing technology and our assessment of the likely remediation actions to be taken. We continue to pursue remediation activities, primarily to address the historical use of oils containing polychlorinated biphenyls (“PCBs”) at our Spokane, Washington (“Trentwood”) facility. Our remediation efforts are in collaboration with the Washington State Department of Ecology (“Ecology”), to which we submitted a feasibility study in 2012 of remediation alternatives and from which we received permission to begin certain remediation activities pursuant to a signed work order. We have completed a number of sections of the work plan and have received satisfactory completion approval from Ecology on those sections. In cooperation with Ecology, we constructed an experimental treatment facility to determine the treatability and evaluate the feasibility of removing PCBs from ground water under the Trentwood facility. In 2015, we began treatment operations involving a walnut shell filtration system, which we optimized for maximum PCB capture during 2020. Furthermore, based on advancements in technology, we signed an Amended Agreed Order with Ecology in 2020 to evaluate and implement new technologies for PCB removal from groundwater on a pilot basis. The primary technology we are evaluating is Ultraviolet Light Advanced Oxidation Process. As the long-term success of the new methodology cannot be reasonably determined at this time, it is possible we may need to make upward adjustments to our related accruals and cost estimates as the long term results become available. Pursuant to a consent agreement with the Ohio Environmental Protection Agency (“OEPA”), we initiated an investigational study of our Newark facility related to historical on-site waste disposal. During the quarter ended December 31, 2018, we submitted our remedial investigation study to the OEPA for review and approval. The final remedial investigation report was approved by the OEPA during the quarter ended December 31, 2020. We are currently preparing the required feasibility study, which we expect to submit to the OEPA for review during the quarter ending June 30, 2021. The actual and final remediation cost estimates will not be fully determinable until the feasibility study has been accepted by the OEPA and the selected remediation design work plans are completed, which we expect to occur in the next 7 to 13 months. At March 31, 2021, our environmental accrual of $18.0 million represented our estimate of the incremental remediation cost based on: (i) proposed alternatives in the final feasibility study related to the Trentwood facility; (ii) currently available facts with respect to our Newark facility; and (iii) facts related to certain other locations owned or formerly owned by us. In accordance with approved and proposed remediation action plans, we expect that the implementation and ongoing monitoring could occur over a period of 30 or more years. As additional facts are developed, feasibility studies are completed, remediation plans are modified, necessary regulatory approvals for the implementation of remediation are obtained, alternative technologies are developed and/or other factors change, there may be revisions to management’s estimates and actual costs may exceed the current environmental accruals. We believe at this time that it is reasonably possible that undiscounted costs associated with these environmental matters may exceed current accruals by amounts that could be, in the aggregate, up to an estimated $11.6 million over the remediation period. It is reasonably possible that our recorded estimate will change in the next 12 months. Warrick Rolling Mill Potential CARO Liability. We identified potential conditional asset retirement obligations (“CAROs”) related to the future removal and disposal of asbestos that is contained within the Warrick Rolling Mill facility. We believe that the asbestos is appropriately contained in accordance with current environmental regulations. If the facility were demolished or subject to renovation activities that disturb the asbestos, certain environmental regulations are in place which specify the manner in which the asbestos must be handled and disposed. We are required to record the fair value of CAROs if they can be reasonably estimated. As of March 31, 2021, we are in the process of evaluating and determining the fair value of a potential CARO, if any, acquired as part of the Warrick Rolling Mill acquisition. No liability has been recorded on our accompanying Consolidated Balance Sheets as the liability is currently indeterminable. We may conclude at a future date that a CARO exists and we could be required to record a liability for the related obligations in amounts that are material to our consolidated financial statements. While we do not currently expect that the CARO liability will be material to our consolidated financial statements, there can be no assurance as to the existence of a CARO obligation and corresponding liabilities that we may be required to record in the future. Other Contingencies. We are party to various lawsuits, claims, investigations and administrative proceedings that arise in connection with past and current operations. We evaluate such matters on a case-by-case basis and our policy is to vigorously contest any such claims we believe are without merit. We accrue for a legal liability when it is both probable that a liability has been incurred and the amount of the loss is reasonably estimable. Quarterly, in addition to when changes in facts and circumstances require it, we review and adjust these accruals to reflect the impacts of negotiations, settlements, rulings, advice of legal counsel and other information and events pertaining to a particular case. While uncertainties are inherent in the final outcome of such matters and it is presently impossible to determine the actual cost that may ultimately be incurred, we believe that we have sufficiently accrued for such matters and that the ultimate resolution of pending matters will not have a material impact on our consolidated financial position, operating results or liquidity.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
Accumulated Other Comprehensive Loss	Mar. 31, 2021
Equity [Abstract]
Accumulated Other Comprehensive Loss	9. Accumulated Other Comprehensive Loss The following table presents the changes in the accumulated balances for each component of AOCI (in millions of dollars): Quarter Ended March 31, 2021 2020 Defined Benefit Pension Plan and Salaried VEBA: Beginning balance $ (19.8 ) $ (33.2 ) Amortization of net actuarial loss 1 0.1 0.1 Amortization of prior service cost 1 0.9 1.2 Less: income tax expense 2 (0.3 ) (0.3 ) Net amortization reclassified from AOCI to Net income 0.7 1.0 Translation impact on Canadian pension plan AOCI balance — 0.1 Other comprehensive income, net of tax 0.7 1.1 Ending balance $ (19.1 ) $ (32.1 ) Available for Sale Securities: Beginning balance $ — $ 0.3 Unrealized gain on available for sale securities — 1.3 Less: income tax expense — (0.3 ) Net unrealized gain on available for sale securities — 1.0 Reclassification of unrealized gain upon sale of available for sale securities 3 — (1.5 ) Less: income tax benefit 2 — 0.3 Net gain reclassified from AOCI to Net income — (1.2 ) Other comprehensive loss, net of tax — (0.2 ) Ending balance $ — $ 0.1 Cash Flow Hedges: Beginning balance $ 1.1 $ (5.6 ) Unrealized gain (loss) on cash flow hedges 13.9 (27.9 ) Less: income tax (expense) benefit (3.3 ) 6.8 Net unrealized gain (loss) on cash flow hedges 10.6 (21.1 ) Reclassification of unrealized (gain) loss upon settlement of cash flow hedges 4 (2.7 ) 7.0 Less: income tax benefit (expense) 2 0.6 (1.8 ) Net (gain) loss reclassified from AOCI to Net income (2.1 ) 5.2 Other comprehensive income (loss), net of tax 8.5 (15.9 ) Ending balance $ 9.6 $ (21.5 ) Fair Value Hedges: Beginning balance $ — $ — Unrealized loss on fair value hedges — (0.8 ) Less: income tax benefit — 0.2 Net unrealized loss on fair value hedges — (0.6 ) Excluded component amortized from OCI to Net income — 0.2 Less: income tax expense 2 — (0.1 ) Net loss reclassified from AOCI to Net income — 0.1 Other comprehensive loss, net of tax — (0.5 ) Ending balance $ — $ (0.5 ) Foreign Currency Translation: Beginning balance $ — $ (0.1 ) Other comprehensive loss, net of tax (0.1 ) — Ending balance $ (0.1 ) $ (0.1 ) Total AOCI ending balance $ (9.6 ) $ (54.1 ) 1 Amounts amortized out of AOCI relating to Salaried VEBA adjustments were included within Other expense, net, as a component of Net periodic postretirement benefit cost relating to Salaried VEBA. 2 Income tax amounts reclassified out of AOCI were included as a component of Income tax benefit (provision). 3 Amounts reclassified out of AOCI relating to sales of available for sale securities were included as a component of Other expense, net. We use the specific identification method to determine the amount reclassified out of AOCI. 4 As of March 31, 2021, we estimate a net mark-to-market loss before tax of $13.3 million in AOCI will be reclassified into Net income upon settlement within the next 12 months.

Restructuring

Restructuring	3 Months Ended
Restructuring	Mar. 31, 2021
Restructuring And Related Activities [Abstract]
Restructuring	10. Restructuring 2020 Plan . In order to align our projected operational requirements with reduced short and mid-term commercial aerospace demand as a result of the Coronavirus Disease 2019 (“COVID-19”) pandemic, we initiated a restructuring plan during the quarter ended June 30, 2020, which consisted primarily of reduction in force measures (“2020 Plan”). Employee costs related to the 2020 Plan were included within Restructuring costs in our Statements of Consolidated Income and consisted of severance, voluntary buyout packages, outplacement services, estimated medical costs and associated payroll costs We have incurred total Restructuring costs of $6.8 million under the 2020 Plan through the quarter ended March 31, 2021. Cash payments associated with the restructuring plan are estimated to extend through 2022. The following table summarizes the changes to our 2020 Plan liabilities during the quarter ended March 31, 2021 (in millions of dollars): Quarter Ended March 31, 2021 Balance as of December 31, 2020 $ 1.4 Cash payments (0.4 ) Other adjustments 1 (0.7 ) Balance as of March 31, 2021 $ 0.3 1 In March 2021, we revised our production forecast for 2021, thereby reducing the estimated number of headcount reductions necessary as compared with our initial restructuring plan. As such, included in Other adjustments is a reduction to our estimated restructuring liability of $0.7 million with an offset to Restructuring costs to accommodate the revised headcount requirements.

Other Expense, Net

Other Expense, Net	3 Months Ended
Other Expense, Net	Mar. 31, 2021
Other Income And Expenses [Abstract]
Other Expense, Net	11. Other Expense Other expense Quarter Ended March 31, 2021 2020 Interest income $ 0.1 $ 0.1 Net periodic postretirement benefit cost relating to Salaried VEBA (0.6 ) (1.2 ) Realized gain on available for sale securities — 1.5 Unrealized loss on equity securities (0.1 ) (0.6 ) All other, net 0.2 (0.6 ) Other expense, net $ (0.4 ) $ (0.8 )

Income Tax Matters

Income Tax Matters	3 Months Ended
Income Tax Matters	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Tax Matters	12. Income Tax Matters The income tax benefit (provision) consisted of the following (in millions of dollars): Quarter Ended March 31, 2021 2020 Domestic $ 0.6 $ (9.5 ) Foreign (0.3 ) (0.1 ) Total $ 0.3 $ (9.6 ) The income tax benefit (provision) 6% of $0.6 million (or 15% of taxable income) for a change in state tax rate due to the Warrick Rolling Mill acquisition; a decrease of $0.4 million (or 10% of taxable income) to the valuation allowance for certain state net operating losses; and (iii) a decrease of $0.2 million (or 6% of taxable income) for the recognition of excess tax benefits from stock-based compensation. There was no material difference between the effective tax rate and the projected blended statutory tax rate for the quarter ended March 31, 2020. Our gross unrecognized benefits relating to uncertain tax positions were $4.0 million $1.5 million We do not expect our gross unrecognized tax benefits to significantly change within the next 12 months.

Net Income Per Share

Net Income Per Share	3 Months Ended
Net Income Per Share	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Income Per Share	13. Net Income Basic net income per share is computed by dividing distributed and undistributed net income allocable to common shares by the weighted-average number of common shares outstanding during the applicable period. The basic weighted-average number of common shares outstanding during the period excludes non-vested share-based payment awards. Diluted net income per share was calculated under the treasury stock method for the quarter ended March 31, 2021 and March 31, 2020, which in both periods was more dilutive than the two-class method. The following table sets forth the computation of basic and diluted net income per share (in millions of dollars, except share and per share amounts): Quarter Ended March 31, 2021 2020 Numerator: Net income $ 4.5 $ 29.1 Denominator – Weighted-average common shares outstanding (in thousands): Basic 15,805 15,838 Add: dilutive effect of non-vested common shares, restricted stock units and performance shares 1 182 170 Diluted 15,987 16,008 Net income per common share, Basic: $ 0.28 $ 1.83 Net income per common share, Diluted: $ 0.28 $ 1.81 1 Quantities in the following discussion are denoted i n whole shares . During the quarter s ended March 31, 2021 and March 31, 2020 , approximately 22,000 shares and 2,000 shares , respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti-dilutive.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
Supplemental Cash Flow Information	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	14. Supplemental Cash Flow Information Quarter Ended March 31, 2021 2020 (In millions of dollars) Interest paid $ 11.7 $ 6.1 Non-cash investing and financing activities (included in Accounts payable): Unpaid purchases of property and equipment $ 2.0 $ 4.7 Supplemental lease disclosures: Operating lease liabilities arising from obtaining operating lease assets $ 13.6 $ 4.2 Cash paid for amounts included in the measurement of operating lease liabilities $ 1.3 $ 1.1 Finance lease liabilities arising from obtaining finance lease assets $ 1.8 $ 0.1 As of March 31, 2021 2020 (In millions of dollars) Components of cash, cash equivalents and restricted cash: Cash and cash equivalents $ 128.0 $ 307.2 Restricted cash included in Other assets 1 13.8 13.9 Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows $ 141.8 $ 321.1 1 We are required to keep on deposit certain amounts that are pledged or held as collateral relating to workers’ compensation and other agreements. We account for such deposits as restricted cash. From time to time, such restricted funds could be returned to us or we could be required to pledge additional cash.

Business, Product and Geographi

Business, Product and Geographical Area Information	3 Months Ended
Business, Product and Geographical Area Information	Mar. 31, 2021
Segment Reporting [Abstract]
Business, Product and Geographical Area Information	15. Business, Product and Geographical Area Information Our primary line of business is the production of semi-fabricated specialty aluminum mill products, such as aluminum plate and sheet and extruded and drawn products, primarily used in aerospace and high strength (“Aero/HS products”), automotive (“Automotive Extrusions”), general engineering (“GE products”) and other industrial (“Other products”). Our acquisition of the Warrick Rolling Mill on March 31, 2021 (see Note 4) will expand our end market applications to include aluminum beverage and food packaging. We operate 13 focused production facilities in the United States and one in Canada. Our chief operating decision maker reviews and evaluates our business as a single operating segment. The following table presents Net sales by end market applications and by timing of control transfer (in millions of dollars): Quarter Ended March 31, 2021 2020 Net sales: Aero/HS products $ 111.7 $ 196.0 Automotive Extrusions 57.6 47.4 GE products 150.4 121.7 Other products 4.3 4.2 Total net sales $ 324.0 $ 369.3 Timing of revenue recognition: Products transferred at a point in time $ 200.2 $ 215.6 Products transferred over time 123.8 153.7 Total net sales $ 324.0 $ 369.3 The following table presents geographic information for income taxes paid (in millions of dollars): Quarter Ended March 31, 2021 2020 Income taxes paid: Domestic $ 0.1 $ — Foreign 0.3 0.1 Total income taxes paid $ 0.4 $ 0.1

Subsequent Events

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events Dividend Declaration. On April 13, 2021, we announced that our Board of Directors declared a quarterly cash dividend of $0.72 per common share. As such, we expect to pay approximately $11.6 million (including dividend equivalents) on or about May 14, 2021 to stockholders of record and the holders of certain restricted stock units at the close of business on April 23, 2021.

Basis of Presentation and Rec_2

Basis of Presentation and Recent Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with United States generally accepted accounting principles (“GAAP”) and the rules and regulations of the Securities and Exchange Commission (“SEC”) applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management’s opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2021 fiscal year. The financial information as of December 31, 2020 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2020. We have reclassified certain amounts in prior-period financial statements to conform to the current period's presentation. On the Consolidated Balance Sheets, prior period presentation of the Canadian pension plan in Long-term liabilities is now reflected in Pension and other postretirement benefits. On the Statements of Consolidated Cash Flows, prior period presentation of Other non-cash changes in assets and liabilities is now reflected in Changes in operating assets and liabilities within the following categories: (i) Prepaid expenses and other current assets; (ii) Accrued liabilities; and (iii) Long-term assets and liabilities, net.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations.
Supply Chain Financing	Supply Chain Financing . Upon our acquisition of the Warrick Rolling Mill (as defined in Note 4 below), we became party to several supply chain financing arrangements, in which we may sell certain of our customers’ trade accounts receivable to such customers’ financial institutions without recourse. We sell our undivided interests in certain of these receivables at our discretion when we determine that the cost of these arrangements is less than the cost of servicing our receivables with existing debt. Under the terms of the agreements, we retain no rights or interest, have no obligations with respect to the sold receivables and do not service the receivables after the sale. As such, these transactions are being accounted for as a sale. Discount fees related to the sale of trade accounts receivable under supply chain financing arrangements will be included in Other expense, net. There were no such discount fees recognized during the quarter ended March 31, 2021.
New Accounting Pronouncements	Adoption of New Accounting Pronouncements In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2019-12, Simplifying the Accounting for Income Taxes Accounting Pronouncements Issued But Not Yet Adopted In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting
Leases	We determine whether an agreement is a lease at inception. We have operating and finance leases for equipment and real estate that primarily have fixed lease payments. Our leases have remaining lease terms of approximately one to 60 years, some of which may include options to extend the lease for up to 60 years and some of which may include options to terminate the lease within one year. For purposes of calculating lease liabilities, these options are included within the lease term when it has become reasonably certain that we will exercise such options . Short-term leases with an initial term of 12 months or less are not recorded on our Consolidated Balance Sheets. As most of our leases do not provide an implicit rate, we use information available at the lease commencement date in determining an incremental borrowing rate when calculating our right-of-use lease assets and liabilities. In determining the inputs to the incremental borrowing rate calculation, we make judgments about the value of the leased asset, our credit rating and the lease term, including the probability of our exercising options to extend or terminate the underlying lease. Additionally, we make judgments around contractual asset substitution rights in determining whether a contract contains a lease. We have lease agreements with lease and non-lease components, which are generally accounted for separately. These non-lease components include items such as common area maintenance, taxes and insurance for our real estate leases, as well as maintenance charges related to our equipment leases. We have, however, applied the practical expedient within ASU 2016-02 to not separate lease and non-lease components to our embedded supply system equipment leases and have therefore accounted for both lease and non‑lease components in determining the lease assets and liabilities. Many of our equipment leases contain clauses that require us to return the equipment with certain functionality intact. We account for these costs as residual value guarantees when the guarantee becomes probable of being owed. Our lease agreements do not contain any material restrictive covenants.

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	3 Months Ended
Supplemental Balance Sheet Information (Tables)	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Supplemental Balance Sheet Information	Supplemental Balance Sheet Information As of March 31, 2021 As of December 31, 2020 (In millions of dollars) Trade Receivables, Net Billed trade receivables $ 306.7 $ 113.6 Allowance for doubtful receivables (0.9 ) (0.8 ) Trade receivables, net $ 305.8 $ 112.8 Inventories 1 Finished products $ 83.0 $ 37.2 Work-in-process 178.5 46.0 Raw materials 117.7 62.3 Operating supplies 6.1 6.5 Total $ 385.3 $ 152.0 Property, Plant and Equipment, Net Land and improvements $ 26.9 $ 21.5 Buildings and leasehold improvements 176.0 117.2 Machinery and equipment 1,144.7 847.4 Construction in progress 2 68.4 37.8 Property, plant and equipment, gross 1,416.0 1,023.9 Accumulated depreciation and amortization (411.1 ) (398.4 ) Assets held for sale 1.7 1.7 Property, plant and equipment, net $ 1,006.6 $ 627.2 Other Accrued Liabilities Uncleared cash disbursements $ 7.0 $ 2.1 Accrued income taxes and other taxes payable 10.4 5.2 Accrued annual contribution to Salaried VEBA — 1.7 Accrued interest 11.5 11.6 Short-term environmental accrual – Note 8 4.0 3.7 Other – Note 3 and Note 6 26.0 17.1 Total $ 58.9 $ 41.4 Long-Term Liabilities Workers' compensation accrual $ 30.2 $ 30.6 Long-term environmental accrual – Note 8 14.0 15.1 Other long-term liabilities 32.1 31.6 Total $ 76.3 $ 77.3 1 At March 31, 2021 and December 31, 2020 the current cost of our inventory exceeded its stated last-in, first-out (“LIFO”) value by $24.0 million and $8.4 million 2 Based on market conditions during the quarter ended March 31, 2021, $20.1 million within Construction in progress as of March 31, 2021 related to temporarily idled projects, all of which are expected to resume at a future date.

Leases (Tables)

Leases (Tables)	3 Months Ended
Leases (Tables)	Mar. 31, 2021
Leases [Abstract]
Schedule of Lease Terms and Discount Rates	The following table presents lease terms and discount rates as of March 31, 2021: Finance Leases Operating Leases Weighted-average lease term (in years) 24.0 7.5 Weighted-average discount rate 3.5 % 4.2 %
Schedule of Lease Assets and Lease Liabilities	The following table summarizes the classification of lease assets and lease liabilities on our Consolidated Balance Sheets (in millions of dollars): Leases Classification As of March 31, 2021 As of December 31, 2020 Assets Operating lease assets Operating lease assets $ 38.9 $ 26.5 Finance lease assets Property, plant and equipment, net 9.6 8.1 Total lease assets $ 48.5 $ 34.6 Liabilities Current: Operating lease liabilities Other accrued liabilities $ 8.1 $ 4.4 Finance lease liabilities Other accrued liabilities 2.0 1.9 Non-current: Operating lease liabilities Long-term portion of operating lease liabilities 34.1 25.6 Finance lease liabilities Long-term liabilities 7.6 6.2 Total lease liabilities $ 51.8 $ 38.1
Components of Lease Cost	The following table summarizes the components of lease cost on our Statements of Consolidated Income (in millions of dollars): Quarter Ended March 31, 2021 2020 Operating lease cost $ 2.0 $ 1.8 Short-term lease cost 0.2 0.3 Finance lease cost: Amortization of leased assets 0.5 0.4 Interest on lease liabilities 0.1 0.1 Total lease cost $ 2.8 $ 2.6
Schedule of Maturity of Our Lease Liabilities	The following table presents the maturity of our lease liabilities as of March 31, 2021 (in millions of dollars): Maturity of Lease Liabilities Finance Leases Operating Leases Remainder of 2021 $ 1.8 $ 7.3 2022 2.1 8.9 2023 1.8 7.5 2024 1.3 6.7 2025 1.1 3.6 Thereafter 6.6 17.0 Total minimum lease payments $ 14.7 $ 51.0 Less: interest (5.1 ) (8.8 ) Present value $ 9.6 $ 42.2

Business Combinations, Goodwi_2

Business Combinations, Goodwill and Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2021
Business Combinations And Goodwill Disclosure [Abstract]
Schedule of Preliminary Purchase Consideration	The preliminary purchase consideration to allocate was determined as follows (in millions of dollars): Contract purchase price $ 670.0 Preliminary working capital adjustment 31.0 Initial outstanding indebtedness – Other postretirement benefits liabilities (83.5 ) Cash paid at acquisition close on March 31, 2021 617.5 Estimate of post-close adjustments (12.7 ) Total preliminary purchase consideration to allocate $ 604.8
Summary of Preliminary Fair Value of Assets Acquired and Liabilities Assumed at Acquisition Date	The following table summarizes the preliminary fair values of assets acquired and liabilities assumed at the acquisition date (in millions of dollars): Trade receivables $ 162.4 Other receivables 6.2 Inventories, including step up 209.0 Property, plant and equipment 385.4 Operating lease assets 12.3 Intangible assets 56.5 Goodwill 27.4 Accounts payable (143.0 ) Accrued salaries, wages and related expenses (5.9 ) Other accrued liabilities (11.5 ) Long-term portion of operating lease liabilities (8.7 ) Pension and other postretirement benefits (83.7 ) Long-term liabilities (1.6 ) Preliminary allocated purchase consideration $ 604.8
Components of Acquired Intangible Assets and Estimated Useful Lives	Intangible Assets. The following table presents the components of acquired intangible assets and their estimated useful lives as of the date of acquisition (in millions of dollars): Useful Life (in years) Fair Value Favorable lease contract 120 $ 7.0 Favorable commodity contracts 2 11.0 Customer relationships 12 38.5 Total $ 56.5
Schedule of Goodwill	The following table presents the changes to goodwill during the quarter ended March 31, 2021 (in millions of dollars): Gross Carrying Value Accumulated Impairment Loss Net Carrying Value Balance as of December 31, 2020 $ 37.2 $ (18.4 ) $ 18.8 Warrick Rolling Mill acquisition 27.4 — 27.4 Balance as of March 31, 2021 $ 64.6 $ (18.4 ) $ 46.2
Unaudited Proforma Information of Consolidated Results of Operations	The unaudited pro forma information presented below is for informational purposes only and is not necessarily indicative of our consolidated results of operations of the consolidated business had the acquisition occurred at the beginning of fiscal year 2020 or of the results of our future operations of the consolidated business. Quarter Ended March 31, 2021 2020 Net sales $ 635.9 $ 636.1 Net income $ 9.9 $ 3.5

Employee Benefits (Tables)

Employee Benefits (Tables)	3 Months Ended
Employee Benefits (Tables)	Mar. 31, 2021
Compensation And Retirement Disclosure [Abstract]
Summary of Assumptions Used to Determine Warrick Rolling Mill Pension and OPEB Obligations	The following table presents the assumptions used to determine the Warrick Rolling Mill pension and OPEB obligations: Warrick Pension Plan Warrick OPEB As of March 31, 2021 As of March 31, 2021 Discount rate 3.24 % 2.97 % Expected long-term return on plan assets 7.00 % N/A Trend rate (initial) N/A 5.40 % Trend rate (ultimate) N/A 4.00 % Years to reach ultimate trend N/A 14 Rate of compensation increase 2.50 % —
Schedule of Expected Benefit Payments	The following table presents the minimum net benefits expected to be paid (in millions of dollars): Year Ended December 31, 2021 2022 2023 2024 2025 2026-2030 Warrick pension plan benefit payments $ 0.1 $ 0.1 $ 0.2 $ 0.3 $ 0.5 $ 4.4 Warrick OPEB plan benefit payments 0.7 1.6 2.3 3.0 3.7 27.2 Total net benefits $ 0.8 $ 1.7 $ 2.5 $ 3.3 $ 4.2 $ 31.6
Schedule of Total Expense Related to Benefit Plans	The following table presents the total expense related to all postretirement benefit plans (in millions of dollars): Quarter Ended March 31, 2021 2020 Defined contribution plans 1 $ 3.4 $ 3.9 Deferred compensation plan 2 — (0.4 ) Multiemployer pension plans 1 1.1 1.3 Net periodic postretirement benefit cost relating to Salaried VEBA 2 0.6 1.2 Total $ 5.1 $ 6.0 1 2
Schedule of Net Benefit Costs	The following table presents the components of Net periodic postretirement benefit cost relating to Salaried VEBA (in millions of dollars): Quarter Ended March 31, 2021 2020 Salaried VEBA 1 Interest cost $ 0.4 $ 0.6 Expected return on plan assets (0.8 ) (0.7 ) Amortization of prior service cost 2 0.9 1.2 Amortization of net actuarial loss 0.1 0.1 Total net periodic postretirement benefit cost relating to Salaried VEBA $ 0.6 $ 1.2 1 2

Derivatives, Hedging Programs_2

Derivatives, Hedging Programs and Other Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Summary of Volume of Derivative and or Physical Delivery Commitments with Energy Companies	The following table summarizes the volume of our derivative and/or physical delivery commitments with energy companies in place to cover our exposure to price fluctuations of our expected variable priced energy purchases as of March 31, 2021: Remainder of 2021 2022 2023 2024 2025 2026 Natural Gas 46% 50% 49% 45% 20% 20% Electricity 96% 76% 44% — — —
Summary of Derivative Positions	The following table summarizes our derivative positions at March 31, 2021: Aluminum Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 4/21 through 12/23 113.5 Fixed price sales contracts 4/21 through 11/21 0.9 Midwest premium swap contracts 1 4/21 through 12/23 69.1 Alloying Metals Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 4/21 through 12/22 9.1 Fixed price sales contracts 4/21 through 12/21 3.2 Natural Gas Maturity Period (month/year) Notional Amount of Contracts (mmbtu) Fixed price purchase contracts 4/21 through 12/24 6,060,000 Electricity Maturity Period (month/year) Notional Amount of Contracts (Mwh) Fixed price purchase contracts 4/21 through 12/22 417,030 1 Regional premiums represent the premium over the London Metal Exchange price for primary aluminum which is incurred on our purchases of primary aluminum.
Summary of (Gain) Loss Associated with Derivative Contracts	The following table summarizes the amount of (gain) loss included on our Statements of Consolidated Income associated with all derivative contracts (in millions of dollars): Quarter Ended March 31, Statements of Consolidated 2021 2020 Income Classification Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of hedges are recorded: Cash flow hedges $ 262.5 $ 286.6 Cost of products sold Fair value hedges n/a $ 13.2 Depreciation and amortization (Gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges: Aluminum $ (2.9 ) $ 5.7 Cost of products sold Alloying Metals (0.9 ) 0.6 Cost of products sold Natural gas — 0.5 Cost of products sold Electricity — 0.2 Cost of products sold Total (gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges $ (3.8 ) $ 7.0 Loss (gain) recognized in our Statements of Consolidated Income related to fair value hedges: Foreign exchange contracts $ — $ 0.2 Depreciation and amortization Hedged item — (0.2 ) Depreciation and amortization Excluded component amortized from AOCI — 0.2 Depreciation and amortization Total loss recognized in our Statements of Consolidated Income related to fair value hedges $ — $ 0.2 Gain recognized in our Statements of Consolidated Income related to non-designated hedges: Alloying Metals – Unrealized gain $ (0.3 ) $ — Cost of products sold Total gain recognized in our Statements of Consolidated Income related to non-designated hedges: $ (0.3 ) $ —
Schedule of Fair Value of Derivative Financial Instruments	The following table presents the fair value of our derivative financial instruments (in millions of dollars): As of March 31, 2021 As of December 31, 2020 Assets Liabilities Net Amount Assets Liabilities Net Amount Cash Flow Hedges: Aluminum – Fixed price purchase contracts $ 8.9 $ (0.1 ) $ 8.8 $ 4.6 $ (0.1 ) $ 4.5 Fixed price sales contracts — (0.1 ) (0.1 ) — — — Midwest premium swap contracts 3.0 — 3.0 0.2 (1.2 ) (1.0 ) Natural gas – Fixed price purchase contracts 0.3 (1.1 ) (0.8 ) 0.2 (1.5 ) (1.3 ) Electricity – Fixed price purchase contracts 3.7 (1.7 ) 2.0 2.0 (2.5 ) (0.5 ) Total cash flow hedges 15.9 (3.0 ) 12.9 7.0 (5.3 ) 1.7 Non-Designated Hedges: Alloying Metals – Fixed price purchase contracts 4.2 (0.1 ) 4.1 3.9 — 3.9 Fixed price sales contracts — (1.2 ) (1.2 ) — (1.3 ) (1.3 ) Total non-designated hedges 4.2 (1.3 ) 2.9 3.9 (1.3 ) 2.6 Total $ 20.1 $ (4.3 ) $ 15.8 $ 10.9 $ (6.6 ) $ 4.3 The following table presents the total amounts of derivative assets and liabilities on our Consolidated Balance Sheets (in millions of dollars): As of March 31, 2021 As of December 31, 2020 Derivative assets: Prepaid expenses and other current assets $ 15.5 $ 8.4 Other assets 4.6 2.5 Total derivative assets $ 20.1 $ 10.9 Derivative liabilities: Other accrued liabilities $ (2.2 ) $ (3.8 ) Long-term liabilities (2.1 ) (2.8 ) Total derivative liabilities $ (4.3 ) $ (6.6 )

Debt and Credit Facility (Table

Debt and Credit Facility (Tables)	3 Months Ended
Debt and Credit Facility (Tables)	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Availability and Usage of Revolving Credit Facility	The following table summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of March 31, 2021 (in millions of dollars except for borrowing rate): Revolving Credit Facility borrowing commitment $ 375.0 Borrowing base availability $ 375.0 Less: Outstanding borrowings under Revolving Credit Facility — Less: Outstanding letters of credit under Revolving Credit Facility (7.8 ) Remaining borrowing availability $ 367.2 Borrowing rate (if applicable) 1 3.50 % 1

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
Accumulated Other Comprehensive Loss (Tables)	Mar. 31, 2021
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table presents the changes in the accumulated balances for each component of AOCI (in millions of dollars): Quarter Ended March 31, 2021 2020 Defined Benefit Pension Plan and Salaried VEBA: Beginning balance $ (19.8 ) $ (33.2 ) Amortization of net actuarial loss 1 0.1 0.1 Amortization of prior service cost 1 0.9 1.2 Less: income tax expense 2 (0.3 ) (0.3 ) Net amortization reclassified from AOCI to Net income 0.7 1.0 Translation impact on Canadian pension plan AOCI balance — 0.1 Other comprehensive income, net of tax 0.7 1.1 Ending balance $ (19.1 ) $ (32.1 ) Available for Sale Securities: Beginning balance $ — $ 0.3 Unrealized gain on available for sale securities — 1.3 Less: income tax expense — (0.3 ) Net unrealized gain on available for sale securities — 1.0 Reclassification of unrealized gain upon sale of available for sale securities 3 — (1.5 ) Less: income tax benefit 2 — 0.3 Net gain reclassified from AOCI to Net income — (1.2 ) Other comprehensive loss, net of tax — (0.2 ) Ending balance $ — $ 0.1 Cash Flow Hedges: Beginning balance $ 1.1 $ (5.6 ) Unrealized gain (loss) on cash flow hedges 13.9 (27.9 ) Less: income tax (expense) benefit (3.3 ) 6.8 Net unrealized gain (loss) on cash flow hedges 10.6 (21.1 ) Reclassification of unrealized (gain) loss upon settlement of cash flow hedges 4 (2.7 ) 7.0 Less: income tax benefit (expense) 2 0.6 (1.8 ) Net (gain) loss reclassified from AOCI to Net income (2.1 ) 5.2 Other comprehensive income (loss), net of tax 8.5 (15.9 ) Ending balance $ 9.6 $ (21.5 ) Fair Value Hedges: Beginning balance $ — $ — Unrealized loss on fair value hedges — (0.8 ) Less: income tax benefit — 0.2 Net unrealized loss on fair value hedges — (0.6 ) Excluded component amortized from OCI to Net income — 0.2 Less: income tax expense 2 — (0.1 ) Net loss reclassified from AOCI to Net income — 0.1 Other comprehensive loss, net of tax — (0.5 ) Ending balance $ — $ (0.5 ) Foreign Currency Translation: Beginning balance $ — $ (0.1 ) Other comprehensive loss, net of tax (0.1 ) — Ending balance $ (0.1 ) $ (0.1 ) Total AOCI ending balance $ (9.6 ) $ (54.1 ) 1 Amounts amortized out of AOCI relating to Salaried VEBA adjustments were included within Other expense, net, as a component of Net periodic postretirement benefit cost relating to Salaried VEBA. 2 Income tax amounts reclassified out of AOCI were included as a component of Income tax benefit (provision). 3 Amounts reclassified out of AOCI relating to sales of available for sale securities were included as a component of Other expense, net. We use the specific identification method to determine the amount reclassified out of AOCI. 4 As of March 31, 2021, we estimate a net mark-to-market loss before tax of $13.3 million in AOCI will be reclassified into Net income upon settlement within the next 12 months.

Restructuring (Tables)

Restructuring (Tables)	3 Months Ended
Restructuring (Tables)	Mar. 31, 2021
Restructuring And Related Activities [Abstract]
Summary of Changes to Our 2020 Plan Liabilities	The following table summarizes the changes to our 2020 Plan liabilities during the quarter ended March 31, 2021 (in millions of dollars): Quarter Ended March 31, 2021 Balance as of December 31, 2020 $ 1.4 Cash payments (0.4 ) Other adjustments 1 (0.7 ) Balance as of March 31, 2021 $ 0.3 1 In March 2021, we revised our production forecast for 2021, thereby reducing the estimated number of headcount reductions necessary as compared with our initial restructuring plan. As such, included in Other adjustments is a reduction to our estimated restructuring liability of $0.7 million with an offset to Restructuring costs to accommodate the revised headcount requirements.

Other Expense, Net (Tables)

Other Expense, Net (Tables)	3 Months Ended
Other Expense, Net (Tables)	Mar. 31, 2021
Other Income And Expenses [Abstract]
Other Expense, Net	Other expense Quarter Ended March 31, 2021 2020 Interest income $ 0.1 $ 0.1 Net periodic postretirement benefit cost relating to Salaried VEBA (0.6 ) (1.2 ) Realized gain on available for sale securities — 1.5 Unrealized loss on equity securities (0.1 ) (0.6 ) All other, net 0.2 (0.6 ) Other expense, net $ (0.4 ) $ (0.8 )

Income Tax Matters (Tables)

Income Tax Matters (Tables)	3 Months Ended
Income Tax Matters (Tables)	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Tax Benefit (Provision)	The income tax benefit (provision) consisted of the following (in millions of dollars): Quarter Ended March 31, 2021 2020 Domestic $ 0.6 $ (9.5 ) Foreign (0.3 ) (0.1 ) Total $ 0.3 $ (9.6 )

Net Income Per Share (Tables)

Net Income Per Share (Tables)	3 Months Ended
Net Income Per Share (Tables)	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Net Income Per Share	The following table sets forth the computation of basic and diluted net income per share (in millions of dollars, except share and per share amounts): Quarter Ended March 31, 2021 2020 Numerator: Net income $ 4.5 $ 29.1 Denominator – Weighted-average common shares outstanding (in thousands): Basic 15,805 15,838 Add: dilutive effect of non-vested common shares, restricted stock units and performance shares 1 182 170 Diluted 15,987 16,008 Net income per common share, Basic: $ 0.28 $ 1.83 Net income per common share, Diluted: $ 0.28 $ 1.81 1 Quantities in the following discussion are denoted i n whole shares . During the quarter s ended March 31, 2021 and March 31, 2020 , approximately 22,000 shares and 2,000 shares , respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti-dilutive.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
Supplemental Cash Flow Information (Tables)	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Cash Flow Information	Quarter Ended March 31, 2021 2020 (In millions of dollars) Interest paid $ 11.7 $ 6.1 Non-cash investing and financing activities (included in Accounts payable): Unpaid purchases of property and equipment $ 2.0 $ 4.7 Supplemental lease disclosures: Operating lease liabilities arising from obtaining operating lease assets $ 13.6 $ 4.2 Cash paid for amounts included in the measurement of operating lease liabilities $ 1.3 $ 1.1 Finance lease liabilities arising from obtaining finance lease assets $ 1.8 $ 0.1 As of March 31, 2021 2020 (In millions of dollars) Components of cash, cash equivalents and restricted cash: Cash and cash equivalents $ 128.0 $ 307.2 Restricted cash included in Other assets 1 13.8 13.9 Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows $ 141.8 $ 321.1 1 We are required to keep on deposit certain amounts that are pledged or held as collateral relating to workers’ compensation and other agreements. We account for such deposits as restricted cash. From time to time, such restricted funds could be returned to us or we could be required to pledge additional cash.

Business, Product and Geograp_2

Business, Product and Geographical Area Information (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of Net Sales by End Market Segment Applications	The following table presents Net sales by end market applications and by timing of control transfer (in millions of dollars): Quarter Ended March 31, 2021 2020 Net sales: Aero/HS products $ 111.7 $ 196.0 Automotive Extrusions 57.6 47.4 GE products 150.4 121.7 Other products 4.3 4.2 Total net sales $ 324.0 $ 369.3 Timing of revenue recognition: Products transferred at a point in time $ 200.2 $ 215.6 Products transferred over time 123.8 153.7 Total net sales $ 324.0 $ 369.3
Schedule of Income Taxes Paid by Geographical Area	The following table presents geographic information for income taxes paid (in millions of dollars): Quarter Ended March 31, 2021 2020 Income taxes paid: Domestic $ 0.1 $ — Foreign 0.3 0.1 Total income taxes paid $ 0.4 $ 0.1

Basis of Presentation and Rec_3

Basis of Presentation and Recent Accounting Pronouncements - Additional Information (Details)	Mar. 31, 2021USD ($)
Significant Accounting Policies [Line Items]
Discount fees recognized	$ 0
ASU No. 2019-12
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted	true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect	true

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Trade Receivables, Net
Allowance for doubtful receivables	$ (0.9)	$ (0.8)
Trade receivables, net	305.8	112.8
Inventories
Finished products	83	37.2
Work-in-process	178.5	46
Raw materials	117.7	62.3
Operating supplies	6.1	6.5
Total	385.3	152
Property, Plant and Equipment, Net
Land and improvements	26.9	21.5
Buildings and leasehold improvements	176	117.2
Machinery and equipment	1,144.7	847.4
Construction in progress	68.4	37.8
Property, plant and equipment, gross	1,416	1,023.9
Accumulated depreciation and amortization	(411.1)	(398.4)
Assets held for sale	1.7	1.7
Property, plant and equipment, net	1,006.6	627.2
Other Accrued Liabilities
Uncleared cash disbursements	7	2.1
Accrued income taxes and other taxes payable	10.4	5.2
Accrued annual contribution to Salaried VEBA		1.7
Accrued interest	11.5	11.6
Short-term environmental accrual	4	3.7
Other	26	17.1
Total	58.9	41.4
Long-Term Liabilities
Workers' compensation accrual	30.2	30.6
Long-term environmental accrual	14	15.1
Other long-term liabilities	32.1	31.6
Total	76.3	77.3
Billed
Trade Receivables, Net
Billed trade receivables	$ 306.7	$ 113.6

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Excess of Replacement or Current Costs over Stated LIFO Value	$ 24	$ 8.4
Construction in progress expected to resume on future date	$ 20.1

Leases - Additional Information

Leases - Additional Information (Details)	3 Months Ended
Leases - Additional Information (Details)	Mar. 31, 2021
Optional extension lease terms	60 years
Lease termination period	1 year
Minimum
Remaining lease terms	1 year
Maximum
Remaining lease terms	60 years

Leases - Schedule of Lease Term

Leases - Schedule of Lease Terms and Discount Rates (Details)	Mar. 31, 2021
Leases [Abstract]
Finance Lease, Weighted Average Remaining Lease Term	24 years
Operating Lease, Weighted Average Remaining Lease Term	7 years 6 months
Finance Lease, Weighted Average Discount Rate, Percent	3.50%
Operating Lease, Weighted Average Discount Rate, Percent	4.20%

Leases - Schedule of Lease Asse

Leases - Schedule of Lease Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease assets	$ 38.9	$ 26.5
Finance lease assets	$ 9.6	$ 8.1
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property, plant and equipment, net	Property, plant and equipment, net
Total lease assets	$ 48.5	$ 34.6
Operating lease liabilities, current	$ 8.1	$ 4.4
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other accrued liabilities	Other accrued liabilities
Finance lease liabilities, current	$ 2	$ 1.9
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other accrued liabilities	Other accrued liabilities
Operating lease liabilities, noncurrent	$ 34.1	$ 25.6
Finance lease liabilities, noncurrent	$ 7.6	$ 6.2
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term liabilities	Long-term liabilities
Total lease liabilities	$ 51.8	$ 38.1

Leases - Components of Lease Co

Leases - Components of Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 2	$ 1.8
Short-term lease cost	0.2	0.3
Amortization of leased assets	0.5	0.4
Interest on lease liabilities	0.1	0.1
Total lease cost	$ 2.8	$ 2.6

Leases - Schedule of Maturity o

Leases - Schedule of Maturity of Our Lease Liabilities (Details) $ in Millions	Mar. 31, 2021USD ($)
Operating Leases
Remainder of 2021	$ 7.3
2022	8.9
2023	7.5
2024	6.7
2025	3.6
Thereafter	17
Total minimum lease payments	51
Less: interest	(8.8)
Present value	42.2
Finance Leases
Remainder of 2021	1.8
2022	2.1
2023	1.8
2024	1.3
2025	1.1
Thereafter	6.6
Total minimum lease payments	14.7
Less: interest	(5.1)
Present value	$ 9.6

Business Combinations, Goodwi_3

Business Combinations, Goodwill and Intangible Assets - Additional Information (Details) - Alcoa Warrick LLC [Member] - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2021
Finite Lived Intangible Assets [Line Items]
Business combination, purchase price	$ 670
Acquisition costs		$ 11

Business Combinations, Goodwi_4

Business Combinations, Goodwill and Intangible Assets - Schedule of Preliminary Purchase Consideration (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2021
Business Acquisition [Line Items]
Cash paid at acquisition close on March 31, 2021		$ 617.5
Alcoa Warrick LLC [Member]
Business Acquisition [Line Items]
Contract purchase price	$ 670
Preliminary working capital adjustment	31
Initial outstanding indebtedness – Other postretirement benefits liabilities	(83.5)
Cash paid at acquisition close on March 31, 2021	617.5
Estimate of post-close adjustments	(12.7)
Total preliminary purchase consideration to allocate	$ 604.8

Business Combinations, Goodwi_5

Business Combinations, Goodwill and Intangible Assets - Summary of Preliminary Fair Value of Assets Acquired and Liabilities Assumed at Acquisition Date (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Intangible assets	$ 56.5
Goodwill	46.2	$ 18.8
Alcoa Warrick LLC [Member]
Finite Lived Intangible Assets [Line Items]
Trade receivables	162.4
Other receivables	6.2
Inventories, including step up	209
Property, plant and equipment	385.4
Operating lease assets	12.3
Intangible assets	56.5
Goodwill	27.4
Accounts payable	(143)
Accrued salaries, wages and related expenses	(5.9)
Other accrued liabilities	(11.5)
Long-term portion of operating lease liabilities	(8.7)
Pension and other postretirement benefits	83.7
Long-term liabilities	(1.6)
Preliminary allocated purchase consideration	$ 604.8

Business Combinations, Goodwi_6

Business Combinations, Goodwill and Intangible Assets - Components of Acquired Intangible Assets and Estimated Useful Lives (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Finite Lived Intangible Assets [Line Items]
Fair Value	$ 56.5
Favorable Lease Contract
Finite Lived Intangible Assets [Line Items]
Useful Life (in years)	120 years
Fair Value	$ 7
Favorable Commodity Contracts
Finite Lived Intangible Assets [Line Items]
Useful Life (in years)	2 years
Fair Value	$ 11
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Useful Life (in years)	12 years
Fair Value	$ 38.5

Business Combinations, Goodwi_7

Business Combinations, Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 64.6	$ 37.2
Accumulated Impairment Loss	(18.4)	(18.4)
Net Carrying Value	46.2	$ 18.8
Alcoa Warrick LLC [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value	27.4
Net Carrying Value	$ 27.4

Business Combinations, Goodwi_8

Business Combinations, Goodwill and Intangible Assets - Unaudited Proforma Information of Consolidated Results of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Business Combinations And Goodwill Disclosure [Abstract]
Net sales	$ 635.9	$ 636.1
Net income	$ 9.9	$ 3.5

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Payment for Other Postretirement Benefits	$ 1,700,000	$ 2,900,000
Warrick Rolling Mill \| Other Accrued Liabilities
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,000,000
Postretirement Health Coverage \| Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Maximum contribution threshold			$ 2,900,000
Payment for Other Postretirement Benefits	1,700,000
Pension Plan \| Warrick Rolling Mill
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	6,700,000
Expected minimum employer contributions in 2021	100,000
Other Postretirement Benefits Plan \| Warrick Rolling Mill
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	78,000,000
Expected minimum employer contributions in 2021	700,000
Level 2 \| Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of deferred compensation assets	9,500,000		$ 9,600,000
Accrued salaries, wages and related expenses
Defined Benefit Plan Disclosure [Line Items]
Accrued salaries, wages and related expenses	$ 2,700,000

Employee Benefits - Summary of

Employee Benefits - Summary of Assumptions Used to Determine Warrick Rolling Mill Pension and OPEB Obligations (Details) - Warrick Rolling Mill	3 Months Ended
	Mar. 31, 2021
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.24%
Expected long-term return on plan assets	7.00%
Rate of compensation increase	2.50%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.97%
Trend rate (initial)	5.40%
Trend rate (ultimate)	4.00%
Years to reach ultimate trend	14 years

Employee Benefits - Expected Be

Employee Benefits - Expected Benefit Payments (Details) $ in Millions	Mar. 31, 2021USD ($)
Defined Benefit Plan Disclosure [Line Items]
2021	$ 0.8
2022	1.7
2023	2.5
2024	3.3
2025	4.2
2026-2030	31.6
Pension Plan \| Warrick Rolling Mill
Defined Benefit Plan Disclosure [Line Items]
2021	0.1
2022	0.1
2023	0.2
2024	0.3
2025	0.5
2026-2030	4.4
Other Postretirement Benefits Plan \| Warrick Rolling Mill
Defined Benefit Plan Disclosure [Line Items]
2021	0.7
2022	1.6
2023	2.3
2024	3
2025	3.7
2026-2030	$ 27.2

Employee Benefits - Summary o_2

Employee Benefits - Summary of Total Expense Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 3.4	$ 3.9
Deferred compensation arrangement with individual, compensation expense		(0.4)
Multiemployer plan, contributions by employer	1.1	1.3
Total other employee benefit plans	5.1	6
Postretirement Health Coverage \| Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Total net periodic postretirement benefit cost relating to Salaried VEBA	$ 0.6	$ 1.2

Employee Benefits - Summary o_3

Employee Benefits - Summary of Components of Net Periodic Postretirement Benefit Cost Relating to Salaried VEBA (Details) - Postretirement Health Coverage - Salaried VEBA - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Salaried VEBA:
Interest cost	$ 0.4	$ 0.6
Expected return on plan assets	(0.8)	(0.7)
Amortization of prior service cost	0.9	1.2
Amortization of net actuarial loss	0.1	0.1
Total net periodic postretirement benefit cost relating to Salaried VEBA	$ 0.6	$ 1.2

Derivatives, Hedging Programs_3

Derivatives, Hedging Programs and Other Financial Instruments - Additional Information (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Collateral posted for net derivatives	$ 0	$ 0
Cash collateral posted from customers	0	0
Designated as Hedging Instrument \| Purchase
Derivative [Line Items]
Derivative net liability	$ 200,000	$ 2,700,000

Derivatives, Hedging Programs_4

Derivatives, Hedging Programs and Other Financial Instruments - Summary of Volume of Derivative and or Physical Delivery Commitments with Energy Companies (Details) - Scenario, Forecast	Dec. 31, 2026	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage	20.00%	20.00%	45.00%	49.00%	50.00%	46.00%
Electricity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage				44.00%	76.00%	96.00%

Derivatives, Hedging Programs_5

Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) mmlb in Millions	3 Months Ended
	Mar. 31, 2021mmlbMMBTUMWh
Purchase \| Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	113.5
Purchase \| Aluminum \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Purchase \| Aluminum \| Maximum
Derivative [Line Items]
Derivative maturity period	2023-12
Purchase \| Midwest premium swap contracts
Derivative [Line Items]
Derivative non-monetary notional amount	69.1
Purchase \| Midwest premium swap contracts \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Purchase \| Midwest premium swap contracts \| Maximum
Derivative [Line Items]
Derivative maturity period	2023-12
Purchase \| Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	9.1
Purchase \| Alloying Metals \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Purchase \| Alloying Metals \| Maximum
Derivative [Line Items]
Derivative maturity period	2022-12
Purchase \| Natural Gas
Derivative [Line Items]
Derivative non-monetary notional amount \| MMBTU	6,060,000
Purchase \| Natural Gas \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Purchase \| Natural Gas \| Maximum
Derivative [Line Items]
Derivative maturity period	2024-12
Purchase \| Electricity
Derivative [Line Items]
Derivative non-monetary notional amount \| MWh	417,030
Purchase \| Electricity \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Purchase \| Electricity \| Maximum
Derivative [Line Items]
Derivative maturity period	2022-12
Sales \| Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	0.9
Sales \| Aluminum \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Sales \| Aluminum \| Maximum
Derivative [Line Items]
Derivative maturity period	2021-11
Sales \| Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	3.2
Sales \| Alloying Metals \| Minimum
Derivative [Line Items]
Derivative maturity period	2021-04
Sales \| Alloying Metals \| Maximum
Derivative [Line Items]
Derivative maturity period	2021-12

Derivatives, Hedging Programs_6

Derivatives, Hedging Programs and Other Financial Instruments - Summary of (Gain) Loss Associated with Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of cash flow hedges are recorded	$ 262.5	$ 286.6
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of fair value hedges are recorded	13.5	13.2
Cost of Products Sold \| Not Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Gain recognized in our Statements of Consolidated Income – Unrealized gain	(0.3)
Cost of Products Sold \| Not Designated as Hedging Instrument \| Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Gain recognized in our Statements of Consolidated Income – Unrealized gain	(0.3)
Depreciation and Amortization \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Foreign exchange contracts		0.2
Cash Flow Hedges
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of cash flow hedges are recorded	262.5	286.6
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	(3.8)	7
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Electricity
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income		0.2
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Aluminum
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	(2.9)	5.7
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Alloying Metals
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	$ (0.9)	0.6
Cash Flow Hedges \| Cost of Products Sold \| Designated as Hedging Instrument \| Natural Gas
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income		0.5
Fair Value Hedges
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of fair value hedges are recorded		13.2
Fair Value Hedges \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income		0.2
Fair Value Hedges \| Depreciation and Amortization \| Designated as Hedging Instrument \| Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Hedged item		(0.2)
Excluded component amortized from AOCI		$ 0.2

Derivatives, Hedging Programs_7

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Fair Value of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Designated as Hedging Instrument \| Purchase
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	$ (0.2)	$ (2.7)
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	20.1	10.9
Derivative liability	(4.3)	(6.6)
Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	20.1	10.9
Derivative liability	(4.3)	(6.6)
Net Amount	15.8	4.3
Fair Value, Measurements, Recurring \| Level 2 \| Not Designated as Hedging Instrument \| Alloying Metals
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	4.2	3.9
Derivative liability	(1.3)	(1.3)
Net Amount	2.9	2.6
Fair Value, Measurements, Recurring \| Level 2 \| Not Designated as Hedging Instrument \| Purchase \| Alloying Metals
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	4.2	3.9
Derivative liability	(0.1)	0
Net Amount	4.1	3.9
Fair Value, Measurements, Recurring \| Level 2 \| Not Designated as Hedging Instrument \| Sales \| Alloying Metals
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liability	(1.2)	(1.3)
Net Amount	(1.2)	(1.3)
Fair Value, Measurements, Recurring \| Cash Flow Hedges \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	15.9	7
Derivative liability	(3)	(5.3)
Net Amount	12.9	1.7
Fair Value, Measurements, Recurring \| Cash Flow Hedges \| Level 2 \| Designated as Hedging Instrument \| Purchase \| Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	8.9	4.6
Derivative liability	(0.1)	(0.1)
Net Amount	8.8	4.5
Fair Value, Measurements, Recurring \| Cash Flow Hedges \| Level 2 \| Designated as Hedging Instrument \| Purchase \| Midwest premium swap contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	3	0.2
Derivative liability	0	(1.2)
Net Amount	3	(1)
Fair Value, Measurements, Recurring \| Cash Flow Hedges \| Level 2 \| Designated as Hedging Instrument \| Purchase \| Natural Gas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0.3	0.2
Derivative liability	(1.1)	(1.5)
Net Amount	(0.8)	(1.3)
Fair Value, Measurements, Recurring \| Cash Flow Hedges \| Level 2 \| Designated as Hedging Instrument \| Purchase \| Electricity
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	3.7	2
Derivative liability	(1.7)	(2.5)
Net Amount	2	(0.5)
Fair Value, Measurements, Recurring \| Cash Flow Hedges \| Level 2 \| Designated as Hedging Instrument \| Sales \| Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liability	(0.1)	0
Net Amount	$ (0.1)	$ 0

Derivatives, Hedging Programs_8

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Total Amounts of Derivative Assets and Liabilities on Balance Sheets (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative asset	$ 20.1	$ 10.9
Derivative liability	(4.3)	(6.6)
Prepaid Expenses and Other Current Assets
Derivative [Line Items]
Derivative asset	15.5	8.4
Other Assets
Derivative [Line Items]
Derivative asset	4.6	2.5
Other Accrued Liabilities
Derivative [Line Items]
Derivative liability	(2.2)	(3.8)
Long-term Liabilities
Derivative [Line Items]
Derivative liability	$ (2.1)	$ (2.8)

Debt and Credit Facility - Addi

Debt and Credit Facility - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	May 01, 2020	Apr. 28, 2020	Nov. 26, 2019
Debt Instrument
Interest expense capitalized	$ 100,000	$ 300,000
Revolving Credit Facility
Debt Instrument
Line of credit facility, maximum borrowing capacity	375,000,000
Senior Notes Due 2025 \| Senior Notes
Debt Instrument
Debt instrument contractual rate (percent)				6.50%	6.50%
Debt issuance, percentage of principal amount				101.00%	100.00%
Debt principal amount				$ 50,000,000	$ 300,000,000
Unamortized debt issuance costs	5,000,000
Interest expense	$ 6,000,000
Effective interest rate (percent)	6.80%
Fair value of outstanding debt	$ 371,300,000		$ 376,800,000
Senior Notes Due 2028 \| Senior Notes
Debt Instrument
Debt instrument contractual rate (percent)						4.625%
Debt issuance, percentage of principal amount						100.00%
Debt principal amount						$ 500,000,000
Unamortized debt issuance costs	6,300,000
Interest expense	$ 6,000,000	$ 6,000,000
Effective interest rate (percent)	4.80%
Fair value of outstanding debt	$ 511,700,000		$ 521,300,000

Debt and Credit Facility - Sche

Debt and Credit Facility - Schedule of Availability and Usage of Revolving Credit Facility (Details) - Revolving Credit Facility	Mar. 31, 2021USD ($)
Line Of Credit Facility [Line Items]
Revolving Credit Facility borrowing commitment	$ 375,000,000
Borrowing base availability	375,000,000
Less: Outstanding borrowings under Revolving Credit Facility	0
Less: Outstanding letters of credit under Revolving Credit Facility	(7,800,000)
Remaining borrowing availability	$ 367,200,000
Borrowing rate (if applicable)	3.50%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021USD ($)
Environmental Contingency
Environmental accrual	$ 18,000,000
Expected period related to remediation expenditures for environmental contingencies period	30 years
Potential increase in environmental costs	$ 11,600,000
Time period within which recorded estimate of its obligation may change	12 months
Liability for conditional asset retirement obligations	$ 0
Minimum
Environmental Contingency
Period for final feasibility study	7 months
Maximum
Environmental Contingency
Period for final feasibility study	13 months

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 732.4	$ 733.9
Other comprehensive income (loss), net of tax	9.1	(15.5)
Ending balance	735	721.1
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(19.8)	(33.2)
Less: income tax (expense) benefit	(0.3)	(0.3)
Net loss (gain) reclassified from AOCI to Net income	0.7	1
Translation impact on Canadian pension plan AOCI balance		0.1
Other comprehensive income (loss), net of tax	0.7	1.1
Ending balance	(19.1)	(32.1)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	0.1	0.1
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	0.9	1.2
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.3
Unrealized gain (loss) on securities		1.3
Less: income tax benefit (expense)		(0.3)
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		1
Reclassification from AOCI		(1.5)
Less: income tax (expense) benefit		0.3
Net loss (gain) reclassified from AOCI to Net income		(1.2)
Other comprehensive income (loss), net of tax		(0.2)
Ending balance		0.1
AOCI, Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1.1	(5.6)
Unrealized gain (loss) on securities	13.9	(27.9)
Less: income tax benefit (expense)	(3.3)	6.8
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges	10.6	(21.1)
Reclassification from AOCI	(2.7)	7
Less: income tax (expense) benefit	0.6	(1.8)
Net loss (gain) reclassified from AOCI to Net income	(2.1)	5.2
Other comprehensive income (loss), net of tax	8.5	(15.9)
Ending balance	9.6	(21.5)
AOCI, Excluded Component of Derivative Qualifying as Fair Value Hedge Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Unrealized gain (loss) on securities		(0.8)
Less: income tax benefit (expense)		0.2
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		(0.6)
Reclassification from AOCI		0.2
Less: income tax (expense) benefit		(0.1)
Net loss (gain) reclassified from AOCI to Net income		0.1
Other comprehensive income (loss), net of tax		(0.5)
Ending balance		(0.5)
AOCI, Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(0.1)
Other comprehensive income (loss), net of tax	(0.1)
Ending balance	(0.1)	(0.1)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18.7)	(38.6)
Other comprehensive income (loss), net of tax	9.1	(15.5)
Ending balance	$ (9.6)	$ (54.1)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Equity [Abstract]
Estimated net mark-to-market loss before tax within next twelve months - cash flow hedges	$ 13.3

Restructuring - Additional Info

Restructuring - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
2020 Plan
Restructuring Cost And Reserve [Line Items]
Restructuring costs	$ 6.8

Restructuring - Summary of Chan

Restructuring - Summary of Changes to Our 2020 Plan Liabilities (Details) - 2020 Plan Liabilities $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Restructuring Cost And Reserve [Line Items]
Beginning balance	$ 1.4
Cash payments	(0.4)
Other adjustments	(0.7)
Ending balance	$ 0.3

Restructuring - Summary of Ch_2

Restructuring - Summary of Changes to Our 2020 Plan Liabilities (Parenthetical) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
2020 Plan Liabilities
Restructuring Cost And Reserve [Line Items]
Reduction to estimated restructuring liability	$ 0.7

Other Expense, Net (Details)

Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended
Other Expense, Net (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Other Income And Expenses [Abstract]
Interest income	$ 0.1	$ 0.1
Net periodic postretirement benefit cost relating to Salaried VEBA	(0.6)	(1.2)
Realized gain on available for sale securities		1.5
Unrealized loss on equity securities	(0.1)	(0.6)
All other, net	0.2	(0.6)
Other expense, net	$ (0.4)	$ (0.8)

Income Tax Matters - Income Tax

Income Tax Matters - Income Tax Benefit (Provision) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Domestic	$ 0.6	$ (9.5)
Foreign	(0.3)	(0.1)
Total	$ 0.3	$ (9.6)

Income Tax Matters - Additional

Income Tax Matters - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income tax benefit (provision)	$ 0.3	$ (9.6)
Effective tax rate (percent)	(6.00%)	25.00%
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses	$ (0.4)
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses (percent)	(10.00%)
Effective tax rate reconciliation, change in state tax rate, amount	$ (0.6)
Effective income tax rate reconciliation, change in state tax rate, percent	(15.00%)
Effective income tax rate reconciliation, tax expense (benefit), share-based payment arrangement, amount	$ (0.2)
Effective income tax rate reconciliation, tax expense (benefit), share-based payment arrangement, percent	(6.00%)
Gross unrecognized tax benefits	$ 4		$ 3.8
Gross unrecognized tax benefits that would impact effective tax rate	$ 1.5		$ 1.5

Net Income Per Share - Schedule

Net Income Per Share - Schedule of Calculation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net income	$ 4.5	$ 29.1
Denominator – Weighted-average common shares outstanding (in thousands):
Basic	15,805,000	15,838,000
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares	182,000	170,000
Diluted	15,987,000	16,008,000
Net income per common share, Basic:	$ 0.28	$ 1.83
Net income per common share, Diluted:	$ 0.28	$ 1.81

Net Income Per Share - Schedu_2

Net Income Per Share - Schedule of Calculation of Basic and Diluted Net Income Per Share (Parenthetical) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount	22,000	2,000

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Interest paid	$ 11.7	$ 6.1
Non-cash investing and financing activities (included in Accounts payable):
Unpaid purchases of property and equipment	2	4.7
Supplemental lease disclosures:
Operating lease liabilities arising from obtaining operating lease assets	13.6	4.2
Cash paid for amounts included in the measurement of operating lease liabilities	1.3	1.1
Finance lease liabilities arising from obtaining finance lease assets	1.8	0.1
Components of cash, cash equivalents and restricted cash:
Cash and cash equivalents	128	307.2	$ 780.3
Restricted cash included in Other assets	13.8	13.9
Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows	$ 141.8	$ 321.1	$ 794.3	$ 278.6

Business, Product and Geograp_3

Business, Product and Geographical Area Information - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021Productionfacility
Domestic
Segment Reporting Information [Line Items]
Number of production facilities	13
Canada
Segment Reporting Information [Line Items]
Number of production facilities	1

Business, Product and Geograp_4

Business, Product and Geographical Area Information - Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net sales:
Net sales	$ 324	$ 369.3
Transferred at Point in Time
Net sales:
Net sales	200.2	215.6
Transferred over Time
Net sales:
Net sales	123.8	153.7
Aero/HS products
Net sales:
Net sales	111.7	196
Automotive Extrusions
Net sales:
Net sales	57.6	47.4
GE products
Net sales:
Net sales	150.4	121.7
Other products
Net sales:
Net sales	$ 4.3	$ 4.2

Business, Product and Geograp_5

Business, Product and Geographical Area Information - Schedule of Income Taxes Paid by Geographical Area (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Taxes Paid By Geographical Area [Line Items]
Income taxes paid	$ 0.4	$ 0.1
Domestic
Income Taxes Paid By Geographical Area [Line Items]
Income taxes paid	0.1	0
Foreign
Income Taxes Paid By Geographical Area [Line Items]
Income taxes paid	$ 0.3	$ 0.1

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 13, 2021	Mar. 31, 2021	Mar. 31, 2020
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)		$ 0.72	$ 0.67
Subsequent Event
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)	$ 0.72
Cash dividends declared	$ 11.6
Cash dividends, declared date	Apr. 13, 2021
Cash dividends, payable date	May 14, 2021
Cash dividends, record date	Apr. 23, 2021