ATI Physical Therapy (ATIP) 10-Q10 May 222022 FY Quarterly reportFinancial data

Company Profile

Cover

Cover - shares	3 Months Ended
Cover - shares	Mar. 31, 2022	May 05, 2022
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
Document Transition Report	false
Entity File Number	001-39439
Entity Registrant Name	ATI Physical Therapy, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-1408039
Entity Address, Address Line One	790 Remington Boulevard
Entity Address, City or Town	Bolingbrook
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60440
City Area Code	630
Local Phone Number	296-2223
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
Entity Common Stock, Shares Outstanding		206,825,028
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Central Index Key	0001815849
Current Fiscal Year End Date	--12-31
Common Class A
Document Information [Line Items]
Title of 12(b) Security	Class A common stock, $0.0001 par value
Trading Symbol	ATIP
Security Exchange Name	NYSE
Redeemable Warrants, each whole warrant exercisable for one share of Class A common stock at an exercise price of $11.50 per share
Document Information [Line Items]
Title of 12(b) Security	Redeemable Warrants, each whole warrant exercisable for one share of Class A common stock at an exercise price of $11.50 per share
Trading Symbol	ATIP WS
Security Exchange Name	NYSE

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 94,797	$ 48,616
Accounts receivable (net of allowance for doubtful accounts of $51,519 and $53,533 at March 31, 2022 and December 31, 2021, respectively)	87,809	82,455
Prepaid expenses	8,706	9,303
Other current assets	6,658	3,204
Total current assets	197,970	143,578
Property and equipment, net	136,776	139,730
Operating lease right-of-use assets	255,372	256,646
Goodwill, net	492,240	608,811
Trade name and other intangible assets, net	372,090	411,696
Other non-current assets	2,811	2,233
Total assets	1,457,259	1,562,694
Current liabilities:
Accounts payable	12,264	15,146
Accrued expenses and other liabilities	59,391	64,584
Current portion of operating lease liabilities	50,651	49,433
Current portion of long-term debt	0	8,167
Total current liabilities	122,306	137,330
Long-term debt, net	477,817	543,799
Warrant liability	2,664	4,341
Contingent common shares liability	21,026	45,360
Deferred income tax liabilities	44,178	67,459
Operating lease liabilities	248,354	250,597
Other non-current liabilities	2,348	2,301
Total liabilities	918,693	1,051,187
Commitments and contingencies (Note 17)
Mezzanine equity:
Series A Senior Preferred Stock, $0.0001 par value; 1.0 million shares authorized; $1,011.67 stated value per share and 0.2 million shares issued and outstanding at March 31, 2022; none issued and outstanding at December 31, 2021	140,340	0
Stockholders' equity:
Class A common stock, $0.0001 par value; 470.0 million shares authorized; 207.4 million shares issued, 197.5 million shares outstanding at March 31, 2022; 207.4 million shares issued, 197.4 million shares outstanding at December 31, 2021	20	20
Treasury stock, at cost, 0.04 million shares and 0.03 million shares at March 31, 2022 and December 31, 2021, respectively	(117)	(95)
Additional paid-in capital	1,373,282	1,351,597
Accumulated other comprehensive income	3,780	28
Accumulated deficit	(984,882)	(847,132)
Total ATI Physical Therapy, Inc. equity	392,083	504,418
Non-controlling interests	6,143	7,089
Total stockholders' equity	398,226	511,507
Total liabilities, mezzanine equity and stockholders' equity	$ 1,457,259	$ 1,562,694

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 51,519	$ 53,533
Preferred stock, par value (dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred stock, shares issued (in shares)	200,000	0
Preferred stock, shares outstanding (in shares)	200,000	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	470,000,000	470,000,000
Common stock, shares Issued (in shares)	207,400,000	207,400,000
Common stock, shares outstanding (in shares)	197,500,000	197,400,000
Treasury stock (in shares)	40,000	30,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Net operating revenue	$ 153,822	$ 149,062
Cost of services:
Salaries and related costs	87,415	80,654
Rent, clinic supplies, contract labor and other	51,615	43,296
Provision for doubtful accounts	5,105	7,171
Total cost of services	144,135	131,121
Selling, general and administrative expenses	30,024	24,726
Goodwill and intangible asset impairment charges	155,741	0
Operating loss	(176,078)	(6,785)
Change in fair value of warrant liability (Note 12)	(1,677)	0
Change in fair value of contingent common shares liability (Note 13)	(24,334)	0
Interest expense, net	8,656	16,087
Interest expense on redeemable preferred stock	0	5,308
Other expense, net	2,781	153
Loss before taxes	(161,504)	(28,333)
Income tax benefit	(23,281)	(10,515)
Net loss	(138,223)	(17,818)
Net loss attributable to non-controlling interests	(473)	1,309
Net loss attributable to ATI Physical Therapy, Inc.	$ (137,750)	$ (19,127)
Loss per share of Class A common stock:
Basic (in dollars per share)	$ (0.70)	$ (0.15)
Diluted (in dollars per share)	$ (0.70)	$ (0.15)
Weighted average shares outstanding:
Basic (in shares)	199,971	128,286
Diluted (in shares)	199,971	128,286
Net patient revenue
Net operating revenue	$ 138,925	$ 132,271
Other revenue
Net operating revenue	$ 14,897	$ 16,791

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net loss	$ (138,223)	$ (17,818)
Other comprehensive income:
Unrealized gain on interest rate swap	3,752	561
Comprehensive loss	(134,471)	(17,257)
Net (loss) income attributable to non-controlling interests	(473)	1,309
Comprehensive loss attributable to ATI Physical Therapy, Inc.	$ (133,998)	$ (18,566)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	As reported	Retrospective application of reverse recapitalization	Common Stock	Common StockAs reported	Common StockRetrospective application of reverse recapitalization	Treasury Stock	Treasury StockAs reported	Treasury StockRetrospective application of reverse recapitalization	Additional Paid-In Capital	Additional Paid-In CapitalAs reported	Additional Paid-In CapitalRetrospective application of reverse recapitalization	Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) IncomeAs reported	Accumulated Other Comprehensive (Loss) IncomeRetrospective application of reverse recapitalization	Accumulated Deficit	Accumulated DeficitAs reported	Accumulated DeficitRetrospective application of reverse recapitalization	Non-Controlling Interests	Non-Controlling InterestsAs reported	Non-Controlling InterestsRetrospective application of reverse recapitalization
Beginning balance (in shares) at Dec. 31, 2020				128,285,514	938,557	127,346,957	0	0	0
Beginning balance at Dec. 31, 2020	$ 901,117	$ 901,117	$ 0	$ 13	$ 9	$ 4	$ 0	$ 0	$ 0	$ 954,728	$ 954,732	$ (4)	$ (1,907)	$ (1,907)	$ 0	$ (68,804)	$ (68,804)	$ 0	$ 17,087	$ 17,087	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	504									504
Other comprehensive income	561												561
Distribution to non-controlling interest holder	(3,575)																		(3,575)
Net loss attributable to non-controlling interests	1,309																		1,309
Net loss attributable to ATI Physical Therapy, Inc.	(19,127)															(19,127)
Ending balance (in shares) at Mar. 31, 2021				128,285,514			0
Ending balance at Mar. 31, 2021	880,789			$ 13			$ 0			955,232			(1,346)			(87,931)			14,821
Beginning balance (in shares) at Dec. 31, 2021				197,409,964			29,791
Beginning balance at Dec. 31, 2021	511,507			$ 20			$ (95)			1,351,597			28			(847,132)			7,089
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of 2022 Warrants	$ 19,725									19,725
Vesting of restricted shares distributed to holders of ICUs (in shares)				75,497
Issuance of common stock upon vesting of restricted stock awards (in shares)				40,613
Tax withholdings related to net share settlement of restricted stock awards (in shares)	10,000			(12,824)			12,824
Tax withholdings related to net share settlement of restricted stock awards	$ (22)						$ (22)
Share-based compensation	1,960									1,960
Other comprehensive income	3,752												3,752
Distribution to non-controlling interest holder	(473)																		(473)
Net loss attributable to non-controlling interests	(473)																		(473)
Net loss attributable to ATI Physical Therapy, Inc.	(137,750)															(137,750)
Ending balance (in shares) at Mar. 31, 2022				197,513,250			42,615
Ending balance at Mar. 31, 2022	$ 398,226			$ 20			$ (117)			$ 1,373,282			$ 3,780			$ (984,882)			$ 6,143

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating activities:
Net loss	$ (138,223)	$ (17,818)
Adjustments to reconcile net loss to net cash used in operating activities:
Goodwill and intangible asset impairment charges	155,741	0
Depreciation and amortization	10,111	9,619
Provision for doubtful accounts	5,105	7,171
Deferred income tax provision	(23,281)	(10,515)
Amortization of right-of-use assets	11,807	11,055
Share-based compensation	1,960	504
Amortization of debt issuance costs and original issue discount	660	1,045
Non-cash interest expense on redeemable preferred stock	0	5,308
Loss on extinguishment of debt	2,809	0
(Gain) loss on disposal and impairment of assets	(219)	221
Change in fair value of warrant liability	(1,677)	0
Change in fair value of contingent common shares liability	(24,334)	0
Changes in:
Accounts receivable, net	(10,459)	(11,148)
Prepaid expenses and other current assets	588	(5,265)
Other non-current assets	14	(112)
Accounts payable	(928)	1,060
Accrued expenses and other liabilities	(544)	(5,686)
Operating lease liabilities	(11,555)	(15,984)
Other non-current liabilities	(37)	473
Medicare Accelerated and Advance Payment Program Funds	(4,269)	0
Net cash used in operating activities	(26,731)	(30,072)
Investing activities:
Purchases of property and equipment	(8,772)	(8,376)
Purchases of intangible assets	0	(650)
Proceeds from sale of property and equipment	114	16
Proceeds from sale of clinics	0	248
Net cash used in investing activities	(8,658)	(8,762)
Financing activities:
Proceeds from long-term debt	500,000	0
Deferred financing costs	(12,952)	0
Original issue discount	10,000	0
Principal payments on long-term debt	(555,048)	(2,042)
Proceeds from issuance of Series A Senior Preferred Stock	144,667	0
Proceeds from issuance of 2022 Warrants	20,333	0
Equity issuance costs and original issue discount	(4,935)	0
Taxes paid on behalf of employees for shares withheld	(22)	0
Distribution to non-controlling interest holders	(473)	(3,575)
Net cash provided by (used in) financing activities	81,570	(5,617)
Changes in cash and cash equivalents:
Net increase (decrease) in cash and cash equivalents	46,181	(44,451)
Cash and cash equivalents at beginning of period	48,616	142,128
Cash and cash equivalents at end of period	94,797	97,677
Supplemental noncash disclosures:
Derivative changes in fair value	(3,752)	(561)
Purchases of property and equipment in accounts payable	2,223	2,161
Other supplemental disclosures:
Cash paid for interest	3,932	14,990
Cash paid for taxes	$ 35	$ 1

Overview of the Company

Overview of the Company	3 Months Ended
Overview of the Company	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Overview of the Company	Overview of the Company ATI Physical Therapy, Inc., together with its subsidiaries (herein referred to as “we,” “the Company,” “ATI Physical Therapy” and “ATI”), is a nationally recognized healthcare company, specializing in outpatient rehabilitation and adjacent healthcare services. The Company provides outpatient physical therapy services under the name ATI Physical Therapy and, as of March 31, 2022, had 922 clinics (as well as 20 clinics under management service agreements) located in 25 states. The Company offers a variety of services within its clinics, including physical therapy to treat spine, shoulder, knee and neck injuries or pain; work injury rehabilitation services, including work conditioning and work hardening; hand therapy; and other specialized treatment services. The Company’s direct and indirect wholly-owned subsidiaries include, but are not limited to, Wilco Holdco, Inc., ATI Holdings Acquisition, Inc. and ATI Holdings, LLC. On June 16, 2021 (the “Closing Date”), a Business Combination transaction (the “Business Combination”) was finalized pursuant to the Agreement and Plan of Merger ("Merger Agreement"), dated February 21, 2021 between the operating company, Wilco Holdco, Inc. (“Wilco Holdco”), and Fortress Value Acquisition Corp. II (herein referred to as "FAII" and "FVAC"), a special purpose acquisition company. In connection with the closing of the Business Combination, the Company changed its name from Fortress Value Acquisition Corp. II to ATI Physical Therapy, Inc. The Company’s common stock is listed on the New York Stock Exchange ("NYSE") under the symbol “ATIP.” The Business Combination was accounted for as a reverse recapitalization in accordance with U.S. generally accepted accounting principles ("GAAP"). Under this method of accounting, FAII is treated as the acquired company and Wilco Holdco is treated as the acquirer for financial statement reporting and accounting purposes. As a result, the historical operations of Wilco Holdco are deemed to be those of the Company. Therefore, the financial statements included in this report reflect (i) the historical operating results of Wilco Holdco prior to the Business Combination; (ii) the combined results of FAII and Wilco Holdco following the Business Combination on June 16, 2021; (iii) the assets and liabilities of Wilco Holdco at their historical cost; and (iv) the Company’s equity structure for all periods presented. The recapitalization of the number of shares of common stock attributable to the Business Combination is reflected retroactively to the earliest period presented and will be utilized for calculating earnings per share in all prior periods presented. No step-up basis of intangible assets or goodwill was recorded in the Business Combination consistent with the treatment of the transaction as a reverse recapitalization of Wilco Holdco, Inc. Refer to Note 3 - Business Combinations and Divestiture for additional information. Impact of COVID-19 and CARES Act The coronavirus ("COVID-19") pandemic in the United States resulted in changes to our operating environment. We continue to closely monitor the impact of COVID-19 on all aspects of our business, and our priorities remain protecting the health and safety of employees and patients, maximizing the availability of services to satisfy patient needs and improving the operational and financial stability of our business. While we expect the disruption caused by COVID-19 and resulting impacts to diminish over time, we cannot predict the length of such impacts, and if such impacts continue for an extended period, it could have a continued effect on the Company’s results of operations, financial condition and cash flows, which could be material. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was signed into law providing reimbursement, grants, waivers and other funds to assist health care providers during the COVID-19 pandemic. The Company has realized benefits under the CARES Act including, but not limited to, the following: • The Company applied for and obtained approval to receive $26.7 million of Medicare Accelerated and Advance Payment Program ("MAAPP") funds during the quarter ended June 30, 2020. During the three months ended March 31, 2022, the Company applied $4.3 million in MAAPP funds against the outstanding liability. Because the Company has not yet met all required performance obligations or performed the services related to the remaining funds, as of March 31, 2022 and December 31, 2021, $8.0 million and $12.3 million of the funds are recorded in accrued expenses and other liabilities, respectively. • The Company elected to defer depositing the employer portion of Social Security taxes for payments due from March 27, 2020 through December 31, 2020, interest-free and penalty-free. Related to these payments, as of March 31, 2022 and December 31, 2021, $5.9 million is included in accrued expenses and other liabilities.

Basis of Presentation and Recen

Basis of Presentation and Recent Accounting Standards	3 Months Ended
Basis of Presentation and Recent Accounting Standards	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Recent Accounting Standards	Basis of Presentation and Recent Accounting Standards The accompanying unaudited condensed consolidated financial statements of the Company were prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial information and in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although the Company believes that the disclosures are adequate to make the information presented not misleading. Management believes the unaudited condensed consolidated financial statements for interim periods presented contain all necessary adjustments to state fairly, in all material respects, the Company's financial position, results of operations and cash flows for the interim periods presented. Operating results for the three months ended March 31, 2022 are not necessarily indicative of the results the Company expects for the entire year. In addition, the influence of seasonality, changes in payor contracts, changes in rate per visit, changes in referral and visit volumes, strategic transactions, labor market dynamics and wage inflation, changes in laws and general economic conditions in the markets in which the Company operates and other factors impacting the Company's operations may result in any period not being comparable to the same period in previous years. Preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts during the reporting period. Actual results could differ from those estimates. The Company reports segment information based on the management approach. The management approach designates the internal reporting used by management for making decisions and assessing performance as the source of the Company’s reportable segments. All of the Company’s operations are conducted within the United States. Our chief operating decision maker (“CODM”) is our Chief Executive Officer, who reviews financial information presented on a consolidated basis for purposes of making decisions, assessing financial performance and allocating resources. We operate our business as one operating segment and therefore we have one reportable segment. For further information regarding the Company's accounting policies and other information, the condensed consolidated financial statements should be read in conjunction with our audited consolidated financial statements and notes thereto for the year ended December 31, 2021 included in our Annual Report on Form 10-K filed with the SEC on March 1, 2022. Recently adopted accounting guidance 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 , which provides optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. This standard was subsequently amended by ASU No. 2021-01, Reference Rate Reform (Topic 848): Scope . This standard is optional and may be applied by entities after March 12, 2020, but no later than December 31, 2022. As of March 31, 2022, the Company has derivative instruments for which the interest rates are indexed to the London InterBank Offered Rate (“LIBOR”). During the period ended March 31, 2022, the Company modified the reference rate index on its hedged items from LIBOR to the Secured Overnight Financing Rate ("SOFR"). The Company elected to apply the hedge accounting expedients related to probability and the assessments of effectiveness for future cash flows to assume that the index upon which future hedged transactions will be based matches the index on the corresponding derivatives, which is LIBOR. The guidance allows for different expedient elections to be made at different points in time. As of March 31, 2022, the Company does not anticipate that this guidance will have a material impact on its consolidated financial statements, however, the Company will continue to assess the potential impact on its future hedging relationships and expedient elections, as applicable. Recent accounting pronouncements In October 2021, the FASB issued ASU 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Liabilities from Contracts with Customers , which provides guidance to improve the accounting for acquired revenue contracts with customers in a business combination by addressing diversity in practice. This ASU is effective for the Company on January 1, 2023, with early adoption permitted, and shall be applied on a prospective basis to business combinations that occur on or after the adoption date. The Company is evaluating the effect that the implementation of this standard may have on the Company's consolidated financial statements, but does not currently expect the impact to be material. In November 2021, the FASB issued ASU 2021-10, Government Assistance (Topic 832): Disclosures by Business Entities about Government Assistance , which provides guidance to increase the transparency of government assistance transactions with business entities that are accounted for by applying a grant or contribution accounting model. This ASU is effective for the Company's annual financial statements to be issued for the year ended December 31, 2022, with early adoption permitted. The Company expects to adopt this new accounting standard in its Annual Report on Form 10-K for the year ended December 31, 2022, and does not expect the adoption of this standard to have a material impact on the Company's consolidated financial statements.

Business Combinations and Dives

Business Combinations and Divestiture	3 Months Ended
Business Combinations and Divestiture	Mar. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Business Combinations and Divestiture	Business Combinations and Divestiture The Business Combination As discussed in Note 1 - Overview of the Company , on June 16, 2021 , a business combination between Wilco Holdco and FAII was consummated, which was accounted for as a reverse recapitalization of Wilco Holdco, Inc. At the time of the Business Combination, stockholders of Wilco Holdco, Inc. received 130.3 million shares of the Company’s Class A common stock, par value $0.0001 per share (the “Common Stock”), for the outstanding shares of Wilco Holdco common stock, par value $0.01 per share, that such stockholders owned. Upon distribution of shares of Common Stock to holders of vested and unvested Incentive Common Units (“ICUs”) granted prior to the Business Combination under the Wilco Acquisition, LP 2016 Equity Incentive Plan, 2.0 million of these shares were restricted subject to vesting requirements, resulting in total unrestricted shares of 128.3 million and an exchange ratio of 136.7 unrestricted shares of ATI Physical Therapy, Inc. for every previously outstanding Wilco Holdco share. Immediately following the Business Combination, there were 207.3 million shares issued and 196.6 million outstanding shares of common stock of ATI Physical Therapy, Inc., consisting of the following (in thousands): Class A Common Shares FAII Class A common stock prior to Business Combination 34,500 FAII Class F common stock prior to Business Combination (1) 8,625 Less: FAII Class A common stock redemptions (8,988) FAII common shares (Class A and Class F) 34,137 Add: Shares issued to Wilco Holdco stockholders (2, 3) 130,300 Add: Shares issued through PIPE investment 30,000 Add: Shares issued to Wilco Holdco Series A Preferred stockholders 12,845 Total shares issued as of the Closing Date of the Business Combination (4) 207,282 Less: Vesting Shares (1) (8,625) Less: Restricted shares (3) (2,014) Total shares outstanding as of the Closing Date of the Business Combination (4) 196,643 (1) Per the Merger Agreement, as of the closing of the Business Combination, all Class F shares converted into the equivalent number of Class A common shares and became subject to certain vesting and forfeiture provisions ("Vesting Shares") as detailed in Note 13 - Contingent Common Shares Liability . (2) Includes 1.2 million unrestricted shares upon distribution to holders of vested ICUs under the Wilco Acquisition, LP 2016 Equity Incentive Plan. (3) Includes 2.0 million restricted shares upon distribution to holders of unvested ICUs under the Wilco Acquisition, LP 2016 Equity Incentive Plan. (4 ) Excludes 15.0 million Earnout Shares, 6.9 million Public Warrants and 3.0 million Private Placement Warrants to purchase Class A common stock. Refer to Note 12 - IPO Warrant Liability and Note 13 - Contingent Common Shares Liability for further details. PIPE investment Concurrently with the closing of the Business Combination, pursuant to Subscription Agreements executed between FAII and certain investors, 30.0 million shares of Class A common stock (the “PIPE” investment) were newly issued in a private placement at a purchase price of $10.00 per share for an aggregate purchase price of $300.0 million. The initial PIPE investment included 7.5 million shares of Class A common stock newly issued to certain investment funds managed by affiliates of Fortress Investment Group LLC (“Fortress”) at a purchase price of $10.00 per share for an aggregate purchase price of $75.0 million. Wilco Holdco Series A Preferred Stock Immediately following the Business Combination, all holders of the previously outstanding shares of Wilco Holdco Series A Preferred Stock received a proportionate share of $59.0 million and 12.8 million shares of ATI Physical Therapy, Inc. Class A common stock based on the terms of the Merger Agreement. Refer to Note 11 - Wilco Holdco Redeemable Preferred Stock for further details. Earnout Shares Subject to the terms and conditions of the Merger Agreement, certain stockholders of Wilco Holdco, Inc. were provided the contingent right to receive, in the aggregate, up to 15.0 million shares of Class A common stock that may be issued pursuant to an earnout arrangement if certain Class A common stock price targets are achieved between the Closing Date and the 10 year anniversary of the Closing Date (“Earnout Shares”). The Earnout Shares are subject to acceleration in the event of a sale or other change in control if the holders of Class A common stock would receive a per share price in excess of the applicable Earnout Shares price target. Refer to Note 13 - Contingent Common Shares Liability and Note 14 - Fair Value Measurements for further details. Vesting Shares Pursuant to the Sponsor Letter Agreement executed in connection with the Merger Agreement, 8.6 million shares of Class F common stock of FAII outstanding immediately prior to the Business Combination converted to potential Class A common shares and became subject to certain vesting and forfeiture provisions (“Vesting Shares”). The Vesting Shares are subject to acceleration in the event of a sale or other change in control if the holders of Class A common stock would receive a per share price in excess of the applicable Vesting Shares price target. Refer to Note 13 - Contingent Common Shares Liability and Note 14 - Fair Value Measurements for further details. IPO Warrants Immediately following the Business Combination, the Company had outstanding Public Warrants to purchase an aggregate of 6.9 million shares of the Company’s Class A common stock ("Public Warrants") and outstanding Private Placement Warrants to purchase an aggregate of 3.0 million shares of the Company's Class A common stock ("Private Placement Warrants") (collectively, the “IPO Warrants”). In conjunction with the B usiness Combination , 3.0 million Private Placement Warrants were transferred and surrendered for no consideration based on terms of the Sponsor Letter Agreement. Refer to Note 12 - IPO Warrant Liability and Note 14 - Fair Value Measurements for further details. The following table reflects the components of cash movement related to the Business Combination, PIPE investment and debt repayments (in thousands): Cash in trust with FAII as of the Closing Date of the Business Combination $ 345,036 Cash used for redemptions of FAII Class A common stock (89,877) FAII transaction costs paid at closing (25,821) Cash inflow from Business Combination 229,338 Wilco Holdco, Inc. transaction costs offset against proceeds (19,233) Net proceeds from FAII in Business Combination 210,105 Cash proceeds from PIPE investment 300,000 Repayment of second lien subordinated loan (231,335) Partial repayment of 2016 first lien term loan (216,700) Cash payment to Wilco Holdco Series A Preferred stockholders (59,000) Wilco Holdco, Inc. transaction costs expensed during 2021 (5,543) Net decrease in cash related to Business Combination, PIPE investment and debt repayments $ (2,473) During 2021, the Company expensed $5.5 million in transaction costs related to the Business Combination, which were classified as selling, general and administrative expenses in the consolidated statement of operations. In addition, $19.2 million of Wilco Holdco, Inc. transaction costs related to the Business Combination were offset against additional paid-in capital in the consolidated statements of changes in stockholders’ equity as these costs were determined to be directly attributable to the recapitalization. Home Health divestiture On August 25, 2021, the Company entered into an agreement to divest its Home Health service line. On October 1, 2021, the transaction closed with a sale price of $7.3 million. The major classes of assets and liabilities associated with the Home Health service line consisted of predominantly accounts receivable, accrued expenses and other liabilities which were not material. 2021 acquisitions During 2021, the Company completed 3 acquisitions consisting of 7 total clinics. The Company paid approximately $4.5 million in cash and $1.4 million in future payment consideration, subject to certain time or performance conditions set out in the purchase agreements, to complete the acquisitions. The acquisitions qualified for purchase accounting treatment under ASC Topic 805, Business Combinations, whereby the purchase price was allocated to the assets acquired and liabilities assumed based upon their estimated fair values on the respective acquisition dates. Of the total amount of consideration, $5.5 million was allocated to goodwill based on management's valuations, which were preliminary and subject to completion of the Company's valuation analysis through the 12 month measurement period. Management finalized its valuation analysis at March 31, 2022 and valuation adjustments to the assets acquired and liabilities assumed were not material. Goodwill represents the future economic benefits arising from the other assets acquired that could not be individually identified and separately recognized, such as assembled workforce, synergies, and location. The entire amount of goodwill recorded from these purchases will be deductible for income tax purposes. Acquisition-related costs to complete the transactions, net operating revenue and net income recognized in 2021 related to the acquisitions were not material, individually and in the aggregate. Unaudited proforma consolidated financial information for the acquisitions have not been included as the results are not material, individually and in the aggregate.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
Revenue from Contracts with Customers	Mar. 31, 2022
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers The following table disaggregates net operating revenue by major service line for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Net patient revenue $ 138,925 $ 132,271 ATI Worksite Solutions (1) 8,651 8,493 Management Service Agreements (1) 3,155 3,497 Other revenue (1) 3,091 4,801 $ 153,822 $ 149,062 (1) ATI Worksite Solutions, Management Service Agreements and Other revenue are included within other revenue on the face of the condensed consolidated statements of operations. The following table disaggregates net patient revenue for each associated payor class as a percentage of total net patient revenue for the periods indicated below: Three Months Ended March 31, 2022 March 31, 2021 Commercial 56.8 % 55.4 % Government 23.6 % 22.6 % Workers’ compensation 13.2 % 16.0 % Other (1) 6.4 % 6.0 % 100.0 % 100.0 %

Goodwill, Trade Name and Other

Goodwill, Trade Name and Other Intangible Assets	3 Months Ended
Goodwill, Trade Name and Other Intangible Assets	Mar. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Trade Name and Other Intangible Assets	Goodwill, Trade Name and Other Intangible Assets Changes in the carrying amount of goodwill consisted of the following (in thousands): Total Goodwill Goodwill at December 31, 2021 (1) $ 608,811 Impairment charges (116,335) Acquisitions (2) (236) Goodwill at March 31, 2022 $ 492,240 (1) Net of accumulated impairment losses of $726.8 million. (2) Represents final valuation adjustments related to 2021 acquisitions. Refer to Note 3 - Business Combinations and Divestiture for additional information. The table below summarizes the Company’s carrying amount of trade name and other intangible assets at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Gross intangible assets: ATI trade name (1) $ 369,954 $ 409,360 Non-compete agreements 2,395 2,405 Other intangible assets 640 640 Accumulated amortization: Accumulated amortization – non-compete agreements (604) (425) Accumulated amortization – other intangible assets (295) (284) Total trade name and other intangible assets, net $ 372,090 $ 411,696 (1) Not subject to amortization. The Company recorded $39.4 million of impairment charges related to the trade name indefinite-lived intangible asset during the three months ended March 31, 2022. Amortization expense for the three months ended March 31, 2022 and 2021 was immaterial. The Company estimates that amortization expense related to intangible assets is expected to be immaterial over the next five fiscal years and thereafter. Interim impairment testing as of March 31, 2022 During the quarter ended March 31, 2022, the Company identified an interim triggering event as a result of factors including potential changes in discount rates and the recent decrease in share price. The Company determined that the combination of these factors constituted an interim triggering event that required further analysis with respect to potential impairment to goodwill, trade name indefinite-lived intangible and other assets. As it was determined that it was more likely than not that the fair value of our trade name indefinite-lived intangible asset was below its carrying value, the Company performed an interim quantitative impairment test as of the March 31, 2022 balance sheet date. The Company utilized the relief from royalty method to estimate the fair value of the trade name indefinite-lived intangible asset. The key assumptions associated with determining the estimated fair value include projected revenue growth rates, the royalty rate, the discount rate and the terminal growth rate. As a result of the analysis, the Company recognized a $39.4 million non-cash interim impairment in the line item goodwill and intangible asset impairment charges in its condensed consolidated statements of operations, which represents the difference between the estimated fair value of the Company’s trade name indefinite-lived intangible asset and its carrying value. The Company evaluated its asset groups, including operating lease right-of-use assets that were evaluated based on clinic-level cash flows and clinic-specific market factors, noting no material impairment. As it was determined that it was more likely than not that the fair value of our single reporting unit was below its carrying value, the Company performed an interim quantitative impairment test. In order to determine the fair value of our single reporting unit, the Company utilized an average of a discounted cash flow analysis and comparable public company analysis. The key assumptions associated with determining the estimated fair value include projected revenue growth rates, earnings before interest, taxes, depreciation and amortization ("EBITDA") margins, the terminal growth rate, the discount rate and relevant market multiples. As a result of the analysis, the Company recognized a $116.3 million non-cash interim impairment in the line item goodwill and intangible asset impairment charges in its condensed consolidated statements of operations, which represented the difference between the estimated fair value of the Company’s single reporting unit and its carrying value. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions, estimates and market factors. Estimating the fair value of the Company’s reporting unit and indefinite-lived intangible assets requires us to make assumptions and estimates regarding our future plans, as well as industry, economic, and regulatory conditions. These assumptions and estimates include projected revenue growth rates, EBITDA margins, terminal growth rates, discount rates, relevant market multiples, royalty rates and other market factors. If current expectations of future growth rates, margins and cash flows are not met, or if market factors outside of our control change significantly, then our reporting unit or indefinite-lived intangible assets might become impaired in the future, negatively impacting our operating results and financial position. As the carrying amounts of goodwill and the Company’s trade name indefinite-lived intangible asset have been impaired as of March 31, 2022 and written down to fair value, those amounts are more susceptible to an impairment risk if there are unfavorable changes in assumptions and estimates.

Property and Equipment

Property and Equipment	3 Months Ended
Property and Equipment	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consisted of the following at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Equipment $ 37,067 $ 36,278 Furniture and fixtures 17,300 17,141 Leasehold improvements 187,489 183,542 Automobiles 19 19 Computer equipment and software 95,855 95,362 Construction-in-progress 4,134 3,793 341,864 336,135 Accumulated depreciation and amortization (205,088) (196,405) Property and equipment, net $ 136,776 $ 139,730 The following table presents the amount of depreciation expense recorded in rent, clinic supplies, contract labor and other and selling, general and administrative expenses in the Company’s condensed consolidated statements of operations for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Rent, clinic supplies, contract labor and other $ 7,086 $ 6,506 Selling, general and administrative expenses 2,835 3,058 Total depreciation expense $ 9,921 $ 9,564

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	3 Months Ended
Accrued Expenses and Other Liabilities	Mar. 31, 2022
Payables and Accruals [Abstract]
Accrued Expenses and Other Liabilities	Accrued Expenses and Other Liabilities Accrued expenses and other liabilities consisted of the following at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Salaries and related costs $ 17,174 $ 27,257 CARES Act funds (1) 13,910 18,179 Accrued professional fees 8,993 5,649 Credit balance due to patients and payors 4,049 4,240 Accrued interest 4,046 — Accrued contract labor 3,520 2,057 Transaction-related costs (2) 303 349 Other payables and accrued expenses 7,396 6,853 Total $ 59,391 $ 64,584 (1) Includes current portion of MAAPP funds received and deferred employer Social Security tax payments. (2) Represents costs related to public readiness initiatives and corporate transactions.

Borrowings

Borrowings	3 Months Ended
Borrowings	Mar. 31, 2022
Debt Disclosure [Abstract]
Borrowings	Borrowings Long-term debt consisted of the following at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Senior Secured Term Loan (1) (due February 24, 2028) $ 500,000 $ — 2016 first lien term loan (2) — 555,048 Less: unamortized debt issuance costs (12,303) (1,935) Less: unamortized original issue discount (9,880) (1,147) Total debt, net 477,817 551,966 Less: current portion of long-term debt — (8,167) Long-term debt, net $ 477,817 $ 543,799 (1) Interest rate of 8.25% at March 31, 2022, with interest payable in designated installments at a variable interest rate. The effective interest rate for the Senior Secured Term Loan was 9.2% at March 31, 2022. (2) Loan balance was repaid in its entirety on February 24, 2022. The effective interest rate for the 2016 first lien term loan was 4.9% at December 31, 2021. 2016 first and second lien credit agreements In connection with the Business Combination on June 16, 2021, the Company paid down $216.7 million of its 2016 first lien term loan. The Company recognized $1.7 million in loss on debt extinguishment related to the derecognition of the proportionate amount of remaining unamortized deferred financing costs and unamortized original issue discount associated with the partial debt repayment. In connection with the Business Combination on June 16, 2021, the Company paid $231.3 million to settle its second lien subordinated term loan. The Company recognized $3.8 million in loss on debt extinguishment related to the derecognition of the remaining unamortized deferred financing costs in conjunction with the debt repayment. On February 24, 2022, the Company paid $555.0 million to settle its existing term loan (the "2016 first lien term loan"). The Company accounted for the transaction as a debt extinguishment and recognized $2.8 million in loss on debt extinguishment related to the derecognition of the remaining unamortized deferred financing costs and unamortized original issue discount in conjunction with the debt repayment. The loss on debt extinguishment associated with the repayment of the 2016 first lien term loan has been reflected in other expense, net in the condensed consolidated statements of operations. 2022 Credit Agreement On February 24, 2022 (the "Refinancing Date"), the Company entered into various financing arrangements to refinance its existing long-term debt (the "2022 Debt Refinancing"). As part of the 2022 Debt Refinancing, ATI Holdings Acquisition, Inc. (the "Borrower"), an indirect subsidiary of ATI Physical Therapy, Inc., entered into a credit agreement among the Borrower, Wilco Intermediate Holdings, Inc. ("Holdings"), as loan guarantor, Barclays Bank PLC, as administrative agent and issuing bank, and a syndicate of lenders (the "2022 Credit Agreement"). The 2022 Credit Agreement provides a $550.0 million credit facility (the "2022 Credit Facility") that is comprised of a $500.0 million senior secured term loan (the "Senior Secured Term Loan") which was fully funded at closing and a $50.0 million "super priority" senior secured revolver (the "Revolving Loans") with a $10.0 million letter of credit sublimit. The 2022 Credit Facility refinanced and replaced the Company's prior credit facility for which Barclays Bank PLC served as administrative agent for a syndicate of lenders. In connection with the 2022 Debt Refinancing, the Company also entered into a preferred stock purchase agreement, consisting of senior preferred stock with detachable warrants to purchase common stock for an aggregate stated value of $165.0 million (collectively, the “Preferred Stock Financing”). See Note 10 - Mezzanine and Stockholders' Equity for further information regarding the Preferred Stock Financing. The Company capitalized debt issuance costs totaling $12.5 million related to the 2022 Credit Facility as well as an original issue discount of $10.0 million, which are amortized over the terms of the respective financing arrangements. The Senior Secured Term Loan matures on February 24, 2028 and bears interest, at the Company's election, at a base interest rate of the Alternate Base Rate ("ABR"), as defined in the agreement, plus an applicable credit spread, or the Adjusted Term SOFR Rate, as defined in the agreement, plus an applicable credit spread. The credit spread is determined based on a pricing grid and the Company's Secured Net Leverage Ratio. As of March 31, 2022, borrowings on the Senior Secured Term Loan bear interest at 3-month SOFR, subject to a 1.0% floor, plus 7.25%. The Company may elect to pay 2.0% interest in-kind at a 0.5% premium during the first year under the agreement. The Revolving Loans are subject to a maximum borrowing capacity of $50.0 million and mature on February 24, 2027. Borrowings on the Revolving Loans bear interest, at the Company's election, at a base interest rate of the ABR, as defined in the agreement, plus an applicable credit spread, or the Adjusted Term SOFR Rate, as defined in the agreement, plus an applicable credit spread. The credit spread is determined based on a pricing grid and the Company's Secured Net Leverage Ratio. The Company capitalized issuance costs of $0.5 million related to the Revolving Loans. Unamortized issuance costs of $0.2 million related to the revolving loans under the 2016 credit agreement were added to the balance of unamortized issuance costs to be amortized over the term of the Revolving Loans pursuant to debt extinguishment accounting guidance. Commitment fees on the Revolving Loans are payable quarterly at 0.5% per annum on the daily average undrawn portion for the quarter and are expensed as incurred. The balances of unamortized issuance costs related to the Revolving Loans and the revolving loans under the 2016 credit agreement, respectively, were $0.7 million as of March 31, 2022, and $0.3 million as of December 31, 2021. The 2022 Credit Facility is guaranteed by certain of the Company’s subsidiaries and is secured by substantially all of the assets of Holdings, the Borrower and the Borrower’s wholly owned subsidiaries, including a pledge of the stock of the Borrower, in each case, subject to customary exceptions. The 2022 Credit Agreement contains customary covenants and restrictions, including financial and non-financial covenants. The financial covenants require the Company to maintain $30.0 million of minimum liquidity at each test date through the first quarter of 2024. Additionally, beginning in the second quarter of 2024, the Company must maintain a Secured Net Leverage Ratio, as defined in the agreement, not to exceed 7.00:1.00. The net leverage ratio covenant decreases in the third quarter of 2024 to 6.75:1.00 and further decreases in the first quarter of 2025 to 6.25:1.00, which remains applicable through maturity. The financial covenants are tested as of each fiscal quarter end for the respective periods. The 2022 Credit Facility contains customary representations and warranties, events of default, reporting and other affirmative covenants and negative covenants, including limitations on indebtedness, liens, investments, negative pledges, dividends, junior debt payments, fundamental changes and asset sales and affiliate transactions. Failure to comply with these covenants and restrictions could result in an event of default under the 2022 Credit Facility, subject to customary cure periods. In such an event, all amounts outstanding under the 2022 Credit Facility, together with any accrued interest, could then be declared immediately due and payable. Under the 2022 Credit Facility the Company may be required to make certain mandatory prepayments upon the occurrence of certain events, including: an event of default, a Prepayment Asset Sale or receipt of Net Insurance Proceeds (as defined in the 2022 Credit Agreement) in excess of $15.0 million, or excess cash flows exceeding certain thresholds (as defined in the 2022 Credit Agreement). The Company had letters of credit totaling $1.2 million under the letter of credit sub-facility on the revolving credit facilities as of March 31, 2022 and December 31, 2021, respectively. The letters of credit auto-renew on an annual basis and are pledged to insurance carriers as collateral. Aggregate maturities of long-term debt at March 31, 2022 are as follows (in thousands): 2022 (remainder of year) $ — 2023 — 2024 — 2025 — 2026 — Thereafter 500,000 Total future maturities 500,000 Unamortized original issue discount and debt issuance costs (22,183) Total debt, net $ 477,817

Share-Based Compensation

Share-Based Compensation	3 Months Ended
Share-Based Compensation	Mar. 31, 2022
Share-based Payment Arrangement [Abstract]
Share-Based Compensation	Share-Based Compensation The Company recognizes compensation expense for all share-based compensation awarded to employees, net of forfeitures, using a fair value-based method. The grant-date fair value of each award is amortized to expense on a straight-line basis over the award’s vesting period. Compensation expense associated with share-based awards is included in salaries and related costs and selling, general and administrative expenses in the accompanying condensed consolidated statements of operations, depending on whether the award recipient is a clinic-level or corporate employee, respectively. Share-based compensation expense is adjusted for forfeitures as incurred. ATI 2021 Equity Incentive Plan The Company adopted the ATI Physical Therapy 2021 Equity Incentive Plan (the "2021 Plan") under which it may grant equity interests of ATI Physical Therapy, Inc., in the form of stock options, stock appreciation rights, restricted stock awards and restricted stock units, to members of management, key employees and independent directors of the Company and its subsidiaries. The Compensation Committee is authorized to make grants and to make various other decisions under the 2021 Plan. The maximum number of shares reserved for issuance under the 2021 Plan is approximately 20.7 million. As of March 31, 2022, approximately 9.4 million shares were available for future grant. 2022 grants During the first quarter of 2022, the Company granted stock options and restricted stock units ("RSUs") to certain employees and independent directors of the Company. For the three months ended March 31, 2022, approximately 5.2 million stock options and 4.5 million RSUs were granted under the 2021 Plan. The weighted average grant date fair values related to the 2022 grants were $1.01 and $2.23 for the stock options and RSUs, respectively. The fair values of each stock option granted was determined using the Black-Scholes option-pricing model. As the Company does not have sufficient historical share option exercise experience for such "plain-vanilla" awards, the expected option term was determined using the simplified method, which is the average of the option's vesting and contractual term. Volatility is measured using the historical volatility of certain comparable companies, using daily log-returns of stock prices, as adjusted for the impact of financial leverage. The risk-free interest rate reflects the U.S. Treasury yield curve in effect at the time of the grant. The following weighted-average assumptions were used for the options granted in 2022: 2022 Weighted-average grant-date fair value of options $1.01 Risk-free interest rate 1.74% Term (years) 6.2 Volatility 61.20% Expected dividend —% As of March 31, 2022, the unrecognized compensation expense related to stock options was $6.2 million, to be recognized over a weighted-average period of 3.6 years, and the unrecognized compensation expense related to RSUs was $9.8 million, to be recognized over a weighted-average period of 2.5 years. Total share-based compensation expense recognized in the three months ended March 31, 2022 was approximately $2.0 million.

Mezzanine and Stockholders' Equ

Mezzanine and Stockholders' Equity	3 Months Ended
Mezzanine and Stockholders' Equity	Mar. 31, 2022
Equity [Abstract]
Mezzanine and Stockholders' Equity	Mezzanine and Stockholders' Equity ATI Physical Therapy, Inc. Series A Senior Preferred Stock In connection with the 2022 Debt Refinancing, the Company issued 165,000 shares of non-convertible preferred stock (the "Series A Senior Preferred Stock") plus 5.2 million warrants to purchase shares of the Company's common stock at an exercise price of $3.00 per share (the "Series I Warrants") and warrants to purchase 6.3 million shares of the Company's common stock at an exercise price equal to $0.01 per share (the "Series II Warrants"). The shares of the Series A Senior Preferred Stock have a par value of $0.0001 per share and an initial stated value of $1,000 per share, for an aggregate initial stated value of $165.0 million. The Company is authorized to issue 1.0 million shares of preferred stock per the Certificate of Designation. As of March 31, 2022, there was 0.2 million shares of Series A Senior Preferred Stock issued and outstanding. The gross proceeds received from the issuance of the Series A Senior Preferred Stock and the Series I and Series II Warrants were $165.0 million, which was allocated among the instruments based on the relative fair values of each instrument. Of the gross proceeds, $144.7 million was allocated to the Series A Senior Preferred Stock, $5.1 million to the Series I Warrants and $15.2 million to the Series II Warrants. The resulting discount on the Series A Senior Preferred Stock will be recognized as a deemed dividend when those shares are subsequently remeasured upon becoming redeemable or probable of becoming redeemable. The Company recognized $2.9 million in issuance costs and $1.4 million of original issue discount related to the Series A Senior Preferred Stock. The following table reflects the components of proceeds related to the Series A Senior Preferred Stock (in thousands): Gross proceeds allocated to Series A Senior Preferred Stock $ 144,667 Less: original issue discount (1,447) Less: issuance costs (2,880) Net proceeds received from issuance of Series A Senior Preferred Stock $ 140,340 The Series A Senior Preferred Stock has priority over the Company's Class A common stock and all other junior equity securities of the Company, and is junior to the Company's existing or future indebtedness and other liabilities (including trade payables), with respect to payment of dividends, distribution of assets, and all other liquidation, winding up, dissolution, dividend and redemption rights. The Series A Senior Preferred Stock carries an initial dividend rate of 12.0% per annum (the "Base Dividend Rate"), payable quarterly in arrears. Dividends will be paid in-kind and added to the stated value of the Series A Senior Preferred Stock. The Company may elect to pay dividends on the Series A Senior Preferred Stock in cash beginning on the third anniversary of the Refinancing Date and, with respect to any such dividends paid in cash, the dividend rate then in effect will be decreased by 1.0%. The Base Dividend Rate is subject to certain adjustments, including an increase of 1.0% per annum on the first day following the fifth anniversary of the Refinancing Date and on each one-year anniversary thereafter, and 2.0% per annum upon the occurrence of either an Event of Noncompliance (as defined in the Certificate of Designation) or a failure by the Company to redeem in full all Series A Senior Preferred Stock upon a Mandatory Redemption Event, which includes a change of control, liquidation, bankruptcy or certain restructurings. The paid in-kind dividends related to the Series A Preferred Stock were $1.9 million as of March 31, 2022. The following table presents the change in the aggregate stated value and stated value per share of the Series A Senior Preferred Stock since the Refinancing Date (in thousands, except per share data): Series A Senior Preferred Stock Aggregate stated value as of February 24, 2022 $ 165,000 Accumulated paid in-kind dividends as of March 31, 2022 1,925 Aggregate stated value as of March 31, 2022 $ 166,925 Preferred shares issued and outstanding as of March 31, 2022 165 Stated value per share as of March 31, 2022 $ 1,011.67 The Company has the right to redeem the Series A Senior Preferred Stock, in whole or in part, at any time (subject to certain limitations on partial redemptions). The Redemption Price (as defined in the Certificate of Designation) for each share of Series A Senior Preferred Stock depends on when such optional redemption takes place, if at all. The Series A Senior Preferred Stock is perpetual and is not mandatorily redeemable at the option of the holders, except upon the occurrence of a Mandatory Redemption Event (as defined in the Certificate of Designation). Upon the occurrence of a Mandatory Redemption Event, to the extent not prohibited by law, the Company is required to redeem all Series A Senior Preferred Stock, in cash, at a price per share equal to the then applicable Redemption Price. Because the Series A Senior Preferred Stock is mandatorily redeemable contingent on certain events outside the Company’s control, the Series A Senior Preferred Stock is classified as mezzanine equity in the Company's condensed consolidated balance sheets. Based on the Company’s assessment of the conditions which would trigger the redemption of the Series A Senior Preferred Stock, the Company has determined that the Series A Senior Preferred Stock is neither currently redeemable nor probable of becoming redeemable. Because the Series A Senior Preferred Stock is classified as mezzanine equity and is not considered redeemable or probable of becoming redeemable, the paid in-kind dividends that are added to the stated value do not impact the carrying value of the Series A Senior Preferred Stock in the Company’s condensed consolidated balance sheets. Should the Series A Senior Preferred Stock become probable of becoming redeemable, the Company will recognize changes in the redemption value of the Series A Senior Preferred Stock immediately as they occur and adjust the carrying amount accordingly at the end of each reporting period. As of March 31, 2022, the redemption value of the Series A Senior Preferred Stock was $166.9 million, which is the stated value. If an Event of Noncompliance occurs, then the holders of a majority of the then outstanding shares of Series A Senior Preferred Stock (the “Majority Holders”) have the right to demand that the Company engage in a sale/refinancing process to consummate a Forced Transaction (as defined in the Certificate of Designation). A Forced Transaction includes a refinancing of the Series A Senior Preferred Stock or a sale of the Company. Upon consummation of any Forced Transaction, to the extent not prohibited by law, the Company is required to redeem all Series A Senior Preferred Stock, in cash, at a price per share equal to the then applicable Redemption Price. Holders of shares of Series A Senior Preferred Stock have no voting rights with respect to the Series A Senior Preferred Stock except as set forth in the Certificate of Designation, other documents entered into in connection with the Purchase Agreement and the transactions contemplated thereby (collectively, the “Transaction Documents”), or as otherwise required by law. For so long as any Series A Senior Preferred Stock is outstanding, the Company is prohibited from taking certain actions without the prior consent of the Majority Holders as set forth in the Certificate of Designation which include: issuing equity securities ranking senior to or pari passu with the Series A Senior Preferred Stock, incurring indebtedness or liens, engaging in affiliate transactions, making restricted payments, consummating investments or asset dispositions, consummating a change of control transaction unless the Series A Senior Preferred Stock is redeemed in full, altering the Company’s organizational documents, and making material changes to the nature of the Company’s business. Holders of Series A Senior Preferred Stock, voting as a separate class, have the right to designate and elect one director to serve on the Company’s board of directors until such time after the Refinancing Date that (i) as of any applicable fiscal quarter end, the Company’s trailing 12-month Consolidated Adjusted EBITDA (as defined in the Certificate of Designation) exceeds $100 million, or (ii) the Lead Purchaser ceases to hold at least 50.1% of the Series A Senior Preferred Stock held by it as of the Refinancing Date. 2022 Warrants In connection with the Preferred Stock Financing, the Company agreed to issue to the preferred stockholders the Series I Warrants entitling the holders thereof to purchase 5.2 million shares of the Company's common stock at an exercise price equal to $3.00 per share, exercisable for 5 years from the Refinancing Date; and the Series II Warrants entitling holders thereof to purchase 6.3 million shares of the Company's common stock, at an exercise price equal to $0.01 per share, exercisable for 5 years from the Refinancing Date (collectively, the "2022 Warrants"). Such number of shares of common stock purchasable pursuant to the 2022 Warrant Agreement (the "2022 Warrant Shares") may be adjusted from time to time as set forth in the 2022 Warrant Agreement. The 2022 Warrants are classified as equity instruments and were initially recorded at an amount equal to the proceeds received from the Preferred Stock Financing allocated among the Series A Senior Preferred Stock, the Series I Warrants, and the Series II Warrants based upon their relative fair values. Of the gross proceeds, $5.1 million was allocated to the Series I Warrants and $15.2 million was allocated to the Series II Warrants. The Company recognized total issuance costs and original issue discount of approximately $0.2 million and $0.5 million related to the Series I Warrants and Series II Warrants, respectively. The following table reflects the components of proceeds related to the 2022 Warrants (in thousands): Series I Warrants Series II Warrants Total Gross proceeds allocated to 2022 Warrants $ 5,101 $ 15,232 $ 20,333 Less: original issue discount (51) (152) (203) Less: issuance costs (102) (303) (405) Net proceeds received from issuance of 2022 Warrants $ 4,948 $ 14,777 $ 19,725 Class A common stock The Company is authorized to issue 470.0 million shares of Class A common stock with a par value of $0.0001 per share. Holders of the Company’s Class A common stock are entitled to one vote for each share on each matter on which they are entitled to vote. At March 31, 2022, there were 207.4 million shares of Class A common stock issued and 197.5 million shares outstanding. As a result of the recapitalization associated with the Business Combination, shares are reflected as if they were issued and outstanding as of the earliest reported period to reflect the new capital structure. At the time of the Business Combination, stockholders of Wilco Holdco, Inc. received 130.3 million shares of the Company’s Class A common stock, par value $0.0001 per share, for the outstanding shares of Wilco Holdco common stock, par value $0.01 per share, that such stockholders owned. Upon distribution of shares to holders of unvested Incentive Common Units granted prior to the Business Combination under the Wilco Acquisition, LP 2016 Equity Incentive Plan, 2.0 million of these shares were restricted subject to vesting requirements, resulting in total unrestricted shares of 128.3 million and an exchange ratio of 136.7 unrestricted shares of ATI Physical Therapy, Inc. for every previously outstanding Wilco Holdco share. As of March 31, 2022, shares of Class A common stock reserved for potential future issuance, on an as-if converted basis, were as follows (in thousands): March 31, 2022 Shares available for grant under the ATI 2021 Equity Incentive Plan 9,395 Earnout Shares reserved 15,000 2022 Warrants outstanding 11,498 IPO Warrants outstanding 9,867 Vesting Shares reserved (1) 8,625 Restricted shares (1,2) 1,248 Total shares of common stock reserved 55,633 (1) Represents shares of Class A common stock legally issued, but not outstanding, as of March 31, 2022. (2) Represents a portion of the 2.0 million restricted shares distributed following the Business Combination to holders of unvested Incentive Common Units under the Wilco Acquisition, LP 2016 Equity Incentive Plan. Treasury stock During the three months ended March 31, 2022, the Company net settled 0.01 million shares of its Class A common stock related to employee tax withholding obligations associated with the Company's share-based compensation program. These shares are reflected at cost as treasury stock in the condensed consolidated financial statements. As of March 31, 2022, there were 0.04 million shares of treasury stock totaling $0.1 million recognized in the condensed consolidated balance sheets.

Wilco Holdco Redeemable Preferr

Wilco Holdco Redeemable Preferred Stock	3 Months Ended
Wilco Holdco Redeemable Preferred Stock	Mar. 31, 2022
Equity [Abstract]
Wilco Holdco Redeemable Preferred Stock	Wilco Holdco Redeemable Preferred Stock On May 10, 2016, Wilco Holdco, Inc. issued shares of Series A Preferred Stock (the “Wilco Holdco preferred stock”) for a total consideration value of $98.0 million. Prior to the Business Combination, the Wilco Holdco preferred stock was a class of equity that had priority over the Common Stock with respect to distribution rights, liquidation rights and dividend rights. The Wilco Holdco preferred stockholders, from and after issuance, were entitled to cumulative preferred dividends at an annual rate per share equal to 10.25% of the original issue price. The dividend rate of the Wilco Holdco preferred stock increased by 0.25% at the end of each fiscal quarter beginning after the second anniversary of the issuance of the Wilco Holdco preferred stock. Based on the terms of the Wilco Holdco preferred stockholder agreement, Wilco Holdco, Inc. was required to redeem all outstanding shares of preferred stock upon the occurrence of certain events, such as those related to full repayment of the 2016 first and second lien credit agreements or a deemed liquidating event. Based on these redemption requirements, the Wilco Holdco preferred stock was classified as debt (redeemable preferred stock) in the Company’s historical consolidated balance sheets. Cumulative dividends related to the Wilco Holdco preferred stock were accrued as preferred dividends that increased the balance of the redeemable preferred stock on the Company’s consolidated balance sheets and were recognized as interest expense on redeemable preferred stock in the Company’s consolidated statements of operations. For the three months ended March 31, 2021, the Company incurred cumulative preferred dividends related to the preferred stock of $5.3 million. No dividends were paid related to the preferred stock. In connection with the Business Combination, holders of the outstanding shares of Wilco Holdco Series A Preferred Stock received a proportionate share of $59.0 million and 12.8 million shares of Class A common stock based on the settlement terms in the Merger Agreement. During 2021, the Company recorded a loss on settlement of redeemable preferred stock in the condensed consolidated statement of operations of $14.0 million based on the value of the cash and equity provided to preferred stockholders in relation to the outstanding redeemable preferred stock liability. As a result of the Business Combination, the balance of redeemable preferred stock was fully settled.

IPO Warrant Liability

IPO Warrant Liability	3 Months Ended
IPO Warrant Liability	Mar. 31, 2022
Other Liabilities Disclosure [Abstract]
IPO Warrant Liability	IPO Warrant Liability The Company has outstanding Public Warrants to purchase an aggregate of 6.9 million shares of the Company’s Class A common stock at an exercise price of $11.50 per share and outstanding Private Placement Warrants to purchase an aggregate of 3.0 million shares of the Company's Class A common stock at an exercise price of $11.50 per share. There were no IPO Warrants exercised during the three months ended March 31, 2022. The Company accounts for its outstanding IPO Warrants in accordance with the guidance contained in Accounting Standards Codification 815-40, Derivatives and Hedging - Contracts on an Entity’s Own Equity, and determined that the IPO Warrants do not meet the criteria for equity treatment thereunder. As such, each IPO Warrant must be recorded as a liability and is subject to re-measurement at each balance sheet date. Refer to Note 14 - Fair Value Measurements for further details. Changes in fair value are recognized in change in fair value of warrant liability in the Company’s condensed consolidated statements of operations. The following table presents the change in the fair value of Private Placement Warrants that is recognized in change in fair value of warrant liability in the condensed consolidated statement of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 1,305 Changes in fair value (504) Fair value, end of period $ 801 The following table presents the changes in the fair value of the Public Warrants that is recognized in change in fair value of warrant liability in the condensed consolidated statements of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 3,036 Changes in fair value (1,173) Fair value, end of period $ 1,863

Contingent Common Shares Liabil

Contingent Common Shares Liability	3 Months Ended
Contingent Common Shares Liability	Mar. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Contingent Common Shares Liability	Contingent Common Shares Liability Earnout Shares Subject to the terms and conditions of the Merger Agreement, certain stockholders of Wilco Holdco, Inc. were provided the contingent right to receive, in the aggregate, up to 15.0 million shares of Class A common stock if, from the closing of the Business Combination until the 10 th anniversary thereof, the dollar volume-weighted average price (“VWAP”) of Class A common stock exceeds certain thresholds. The Earnout Shares vest in three equal tranches of 5.0 million shares each if the VWAP of Class A common stock exceeds $12.00, $14.00 and $16.00 per share, respectively, over the designated period of time. The Company accounts for the potential Earnout Shares as a liability in accordance with the guidance in ASC 480, Distinguishing Liabilities from Equity , and ASC 815, Derivatives and Hedging, and is subject to re-measurement at each balance sheet date. Changes in fair value are recognized in the Company’s condensed consolidated statements of operations. As of March 31, 2022, no Earnout Shares have been issued as none of the corresponding share price thresholds have been met. The following table presents the changes in the fair value of the Earnout Shares that is recognized in change in fair value of contingent common shares liability in the condensed consolidated statements of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 28,800 Changes in fair value (15,450) Fair value, end of period $ 13,350 Refer to Note 14 - Fair Value Measurements for further details. Vesting Shares Subject to the terms and conditions of the Sponsor Letter Agreement that was executed in connection with the Merger Agreement, 8.6 million shares of Class F common stock of FAII outstanding immediately prior to the Business Combination converted to potential Class A common shares and became subject to vesting and forfeiture provisions. The Vesting Shares vest in three equal tranches of 2.9 million shares each if the VWAP of Class A common stock exceeds $12.00, $14.00 and $16.00 per share, respectively, over the designated period of time. The Company accounts for the Vesting Shares as a liability in accordance with the guidance in ASC 480, Distinguishing Liabilities from Equity , and ASC 815, Derivatives and Hedging, and is subject to re-measurement at each balance sheet date. Changes in fair value are recognized in the Company’s condensed consolidated statements of operations. As of March 31, 2022, no Vesting Shares are outstanding as none of the corresponding share price thresholds have been met. The following table presents the changes in the fair value of the Vesting Shares that is recognized in change in fair value of contingent common shares liability in the condensed consolidated statements of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 16,560 Changes in fair value (8,884) Fair value, end of period $ 7,676 Refer to Note 14 - Fair Value Measurements for further details.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
Fair Value Measurements	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company determines fair value measurements used in its condensed consolidated financial statements based upon the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels, with Level 1 having the highest priority and Level 3 having the lowest. • Level 1: Observable inputs, which include unadjusted quoted prices in active markets for identical instruments. • Level 2: Observable inputs other than Level 1 inputs, such as quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instruments. • Level 3: Unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions, such as valuations derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. As of March 31, 2022 and December 31, 2021 , respectively, the recorded values of cash and cash equivalents, accounts receivable, other current assets, accounts payable, accrued expenses and deferred revenue approximate their fair values due to the short-term nature of these items. The Company's Senior Secured Term Loan and Revolving Loans are Level 2 fair value measures which have variable interest rates and, a s of March 31, 2022, the recorded amounts approximate fair value. The Company utilizes the market approach valuation technique based on interest rates that are currently available to the Company for issuance of debt with similar terms or maturities. Fair value measurement of share-based financial liabilities The Company determined the fair value of the Public Warrant liability using Level 1 inputs. The Company determined the fair value of the Private Placement Warrant liability using the price of the Public Warrants as a Level 2 input. The Company determined the fair value of the Earnout Shares liability and Vesting Shares liability using Level 3 inpu ts. The contingent common shares contain specific market conditions to determine whether the shares vest based on the Company’s common stock price over a specified measurement period. Given the path-dependent nature of the requirement in which the shares are earned, a Monte-Carlo simulation was used to estimate the fair value of the liability. The Company’s common stock price was simulated to each measurement period based on the above methodology. In each iteration, the simulated stock price was compared to the conditions under which the shares vest. In iterations where the stock price corresponded to shares vesting, the future value of the vesting shares was discounted back to present value. The fair value of the liability was estimated based on the average of all iterations of the simulation. Inherent in a Monte Carlo valuation model are assumptions related to expected stock-price volatility, expected term, risk-free interest rate and dividend yield. The Company estimates the volatility based on the historical volatility of certain guideline companies as of the valuation date. The risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve on the grant date for a maturity similar to the expected term of the Earnout Shares and Vesting Shares. The dividend yield percentage is zero based on the Company's current expectations related to the payment of dividends during the expected term of the Earnout Shares or Vesting Shares. The key inputs into the Monte Carlo option pricing model were as follows as of March 31, 2022 and December 31, 2021 for the respective Level 3 instruments : Earnout Shares Vesting Shares March 31, 2022 December 31, 2021 March 31, 2022 December 31, 2021 Risk-free interest rate 2.33% 1.50% 2.33% 1.50% Volatility 50.82% 44.86% 50.82% 44.86% Dividend yield —% —% —% —% Expected term (years) 9.2 9.5 9.2 9.5 Share price $1.88 $3.39 $1.88 $3.39 Refer to Note 13 - Contingent Common Shares Liability for further details on the change in fair value of the Earnout Shares and Vesting Shares.

Income Taxes

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate and income tax benefit for the three months ended March 31, 2022 were 14.4% and $23.3 million, compared to an effective tax rate and income tax benefit of 37.1% and $10.5 million for the three months ended March 31, 2021. The effective tax rate for the three months ended March 31, 2022 was estimated based on full-year 2022 forecast. The estimated effective tax rate was different than the statutory rate primarily due to book impairment of goodwill. There was no basis in a significant component of the goodwill impaired for tax purposes. Therefore, a portion of the book impairment charge will never create a deduction for tax purposes in any period. As a result, this permanent difference has a substantial impact on the effective tax rate. The estimated effective tax rate applicable to year-to-date losses, in addition to discretes, resulted in a tax benefit of $23.3 million for the three months ended March 31, 2022. The effective tax rate for the three months ended March 31, 2021 was estimated based on full-year 2021 forecast. The effective tax rate was different than the statutory rate primarily due to nondeductible transactions costs and interest expense on redeemable preferred stock. The estimated effective tax rate applicable to year-to-date losses resulted in a tax benefit of $10.5 million for the three months ended March 31, 2021.

Leases

Leases	3 Months Ended
Leases	Mar. 31, 2022
Leases [Abstract]
Leases	Leases The Company leases various facilities and office equipment for its physical therapy operations and administrative support functions under operating leases. The Company’s initial operating lease terms are generally between 7 and 10 years, and typically contain options to renew for varying terms. Right-of-use ("ROU") assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The amortization of operating lease ROU assets and the accretion of operating lease liabilities are reported together as fixed lease expense. The fixed lease expense is recognized on a straight-line basis over the life of the lease. Lease costs are included as components of cost of services and selling, general and administrative expenses on the condensed consolidated statements of operations. Lease costs incurred by lease type were as follows for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Lease cost Operating lease cost $ 16,703 $ 15,823 Variable lease cost (1) 5,205 4,936 Total lease cost (2) $ 21,908 $ 20,759 (1) Includes short term lease costs, which are immaterial . (2) Sublease income was immaterial . During the three months ended March 31, 2022 and 2021, the Company modified the lease terms for a significant number of its real estate leases, primarily related to lease term extensions and renewals in the normal course of business. Modifications during the three months ended March 31, 2022 and 2021 resulted in an increase to the Company’s operating lease ROU assets and operating lease liabilities of approximately $5.7 million and $3.8 million, respectively. Other supplemental quantitative disclosures were as follows for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 16,438 $ 16,166 Cash payments related to lease terminations $ — $ 4,570 Right-of-use assets obtained in exchange for new operating lease liabilities $ 5,142 $ 5,399 Average lease terms and discount rates as of March 31, 2022 and December 31, 2021 were as follows: March 31, 2022 December 31, 2021 Weighted-average remaining lease term: Operating leases 6.3 years 6.4 years Weighted-average discount rate: Operating leases 6.5% 6.5% Estimated undiscounted future lease payments under non-cancellable operating leases, along with a reconciliation of the undiscounted cash flows to operating lease liabilities, respectively, at March 31, 2022 were as follows (in thousands): Year 2022 (remainder of year after March 31, 2022) $ 50,865 2023 66,781 2024 59,498 2025 50,358 2026 44,009 Thereafter 97,574 Total undiscounted future cash flows 369,085 Less: Imputed Interest (70,080) Present value of future cash flows $ 299,005 Presentation on Balance Sheet Current $ 50,651 Non-current $ 248,354

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies From time to time, the Company is a party to legal proceedings, governmental audits and investigations that arise in the ordinary course of business. Management is not aware of any legal proceedings, governmental audits and investigations of which the outcome is probable or reasonably possible to have a material adverse effect on the Company’s results of operations or financial condition, which would require disclosure of the contingency and the possible range of loss. The outcome of any litigation and claims against the Company cannot be predicted with certainty, and the resolution of current or future claims could materially affect our future results of operations, cash flows, or financial position. Shareholder class action complaints On August 16, 2021, two purported ATI shareholders, Kevin Burbige and Ziyang Nie, filed a putative class action complaint in the U.S. District Court for the Northern District of Illinois against ATI; Labeed Diab, Joe Jordan, and Drew McKnight (collectively, the “ATI Individual Defendants”); and Joshua Pack, Marc Furstein, Leslee Cowen, Aaron Hood, Carmen Policy, Rakefet Russak-Aminoach, and Sunil Gulati (collectively, the “FVAC Defendants”). The Burbige/Nie complaint asserted claims against: (i) ATI and the ATI Individual Defendants under Section 10(b) of the Securities Exchange Act of 1934 (the “Exchange Act”); (ii) the ATI Individual Defendants under Section 20(a) of the Exchange Act; and (iii) all defendants under Section 14(a) of the Exchange Act. Plaintiffs Burbige and Nie purported to assert their claims on behalf of those ATI shareholders who purchased or otherwise acquired their ATI shares between April 1, 2021 and July 23, 2021, inclusive, and/or held FVAC Class A common shares as of May 24, 2021 and were eligible to vote at FVAC’s June 15, 2021 special meeting. On October 7, 2021, another purported ATI shareholder, City of Melbourne Firefighters' Retirement System ("City of Melbourne"), filed a putative class action complaint in the U.S. District Court for the Northern District of Illinois against ATI, the ATI Individual Defendants, and the FVAC Defendants. Like the Burbige/Nie complaint, the City of Melbourne complaint asserted claims against (i) ATI and the ATI Individual Defendants under Section 10(b) of the Exchange Act; (ii) the ATI Individual Defendants under Section 20(a) of the Exchange Act; and (iii) all defendants under Section 14(a) of the Exchange Act. City of Melbourne purported to assert its claims on behalf of those ATI shareholders who purchased or otherwise acquired their ATI shares between February 22, 2021 and July 23, 2021, inclusive, and/or held FVAC Class A common shares as of May 24, 2021 and were eligible to vote at FVAC’s June 15, 2021 special meeting. On November 18, 2021, the court consolidated the cases and appointed The Phoenix Insurance Company Ltd. and The Phoenix Pension & Provident Funds as Lead Plaintiffs (“Lead Plaintiffs”) and Pomerantz LLP as Lead Counsel. On February 8, 2022, Lead Plaintiffs filed a consolidated amended complaint against ATI, the ATI Individual Defendants, and the FVAC Defendants, which asserts claims against (i) ATI and the ATI Individual Defendants under Section 10(b) of the Exchange Act; (ii) the ATI Individual Defendants under Section 20(a) of the Exchange Act (in connection with the Section 10(b) claim); (iii) all defendants under Section 14(a) of the Exchange Act; and (iv) the ATI Individual Defendants and the FVAC Defendants under Section 20(a) of the Exchange Act (in connection with the Section 14(a) claim). Lead Plaintiffs purport to assert these claims on behalf of those ATI shareholders who purchased or otherwise acquired their ATI shares between February 22, 2021 and October 19, 2021, inclusive, and/or held FVAC Class A common shares as of May 24, 2021 and were eligible to vote at FVAC’s June 15, 2021 special meeting. The consolidated amended complaint, like the predecessor Burbige/Nie and City of Melbourne complaints, generally alleges that the proxy materials for the FVAC/ATI merger, as well as other ATI disclosures (including the press release announcing ATI’s financial results for the first quarter of 2021), were false and misleading (and, thus, in violation of Sections 10(b) and 14(a) of the Exchange Act) because they failed to disclose that: (i) ATI was experiencing attrition among its physical therapists; (ii) ATI faced increasing competition for clinicians in the labor market; (iii) as a result, ATI faced difficulty retaining therapists and incurred increased labor costs; (iv) also as a result, ATI would open fewer new clinics; and (v) also as a result, the defendants’ positive statements about ATI’s business, operations, and prospects were materially misleading and/or lacked a reasonable basis. Lead Plaintiffs, on behalf of themselves and the putative class, seek money damages in an unspecified amount and costs and expenses, including attorneys’ and experts’ fees. On April 11, 2022, defendants filed motions to dismiss the consolidated amended complaint, which remains pending. As of March 31, 2022, the Company has determined that potential liabilities related to the consolidated amended complaint are not considered probable or reasonably estimable at this time. Shareholder derivative complaint On December 1, 2021, another purported ATI shareholder, Hamza Ghaith, filed a derivative action, purportedly on behalf of ATI, in the U.S. District Court for the Northern District of Illinois against Labeed Diab, Joe Jordan, John Larsen, John Maldonado, Carmine Petrone, Joanne Burns, Christopher Krubert, James Parisi, Drew McKnight, Joshua Pack, Aaron Hood, Carmen Policy, Marc Furstein, Leslee Cowen, Rafeket Russak-Aminoach, and Sunil Gulati (collectively, the “Individual Defendants”). The Ghaith complaint asserts claims on behalf of ATI against: (i) the Individual Defendants for breach of fiduciary duty; (ii) Labeed Diab, Joe Jordan, and Drew McKnight for contribution under Sections 10(b) and 21(d) of the Exchange Act; and (iii) Drew McKnight, Joshua Pack, Aaron Hood, Carmen Policy, Marc Furstein, Leslee Cowen, Rafeket Russak-Aminoach, and Sunil Gulati under Section 14(a) of the Exchange Act. Plaintiff Ghaith’s allegations generally mirror those asserted in the securities complaints described above, and the Ghaith complaint seeks damages in an unspecified amount, certain corporate governance reforms, restitution from the Individual Defendants and disgorgement of all of their compensation, and costs and expenses, including attorneys’ and experts’ fees. As of March 31, 2022, the Company has determined that potential liabilities related to the Ghaith complaint are not considered probable or reasonably estimable at this time. Defendants have not yet responded to the Ghaith complaint. Regulatory matters On November 5, 2021, the Company received from the SEC a voluntary request for the production of documents relating to the earnings forecast and financial information referenced in the Company's July 26, 2021 Form 8-K and related matters. The Company is cooperating with the SEC in connection with this request. Indemnifications The Company has agreed to indemnify its current and former directors and executive officers for costs associated with any fees, expenses, judgments, fines and settlement amounts incurred by them in any action or proceeding to which any of them are, or are threatened to be, made a party by reason of their service as a director or officer. The Company maintains director and officer insurance coverage that would generally enable it to recover a portion of any future amounts paid. The ultimate cost of potential future litigation may exceed the Company’s current insurance coverages and may have a material adverse impact on our results of operations, cash flows and financial condition. The Company also may be subject to indemnification obligations by law with respect to the actions of its employees under certain circumstances and in certain jurisdictions.

Loss per Share

Loss per Share	3 Months Ended
Loss per Share	Mar. 31, 2022
Earnings Per Share [Abstract]
Loss per Share	Loss per Share Basic loss per share is computed by dividing net loss by the weighted average number of common shares outstanding during the period. For the three months ended March 31, 2021, shares of Wilco Holdco preferred stock are treated as participating securities and therefore are included in computing earnings per common share using the two-class method. The two-class method is an earnings allocation formula that calculates basic and diluted net earnings per common share for each class of common stock separately based on dividends declared and participation rights in undistributed earnings as if the earnings for the year had been distributed. As the Wilco Holdco preferred stockholders do not participate in losses, for any periods with a net loss, there is no allocation to participating securities in the period. As of the closing of the Business Combination, the Wilco Holdco preferred stock is no longer outstanding. For the three months ended March 31, 2022, the income available to common shareholders is reduced by the amount of the cumulative dividend for the Series A Senior Preferred Stock that was issued as part of the 2022 Debt Refinancing. The calculation of both basic and diluted loss per share for the periods indicated below was as follows (in thousands, except per share data): Three Months Ended March 31, 2022 March 31, 2021 Basic and diluted loss per share: Net loss $ (138,223) $ (17,818) Less: Net (loss) income attributable to non-controlling interests (473) 1,309 Less: Series A Senior Preferred cumulative dividend 1,925 — Loss available to common stockholders $ (139,675) $ (19,127) Weighted average shares outstanding (1,2) 199,971 128,286 Basic and diluted loss per share $ (0.70) $ (0.15) (1) The weighted-average number of shares outstanding in periods presented prior to the closing of the Business Combination has been retrospectively adjusted based on the exchange ratio established through the transaction. (2) Included within weighted average shares outstanding following the 2022 Debt Refinancing are common shares issuable upon the exercise of the Series II Warrants, as the Series II Warrants are exercisable at any time for nominal consideration. As such, the shares are considered to be outstanding for the purpose of calculating basic and diluted loss per share. For the periods presented, the following securities were not required to be included in the computation of diluted shares outstanding, as their impact would have been anti-dilutive. Figures presented are based on the number of underlying Class A common shares following the Business Combination (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Series I Warrants 5,226 — IPO Warrants 9,867 — Restricted shares (1) 1,248 — Stock options 5,951 — RSUs 4,886 — RSAs 366 — Total 27,544 — (1) Represents a portion of the 2.0 million restricted shares distributed following the Business Combination to holders of unvested Incentive Common Units under the Wilco Acquisition, LP 2016 Equity Incentive Plan. 15.0 million Earnout Shares and 8.6 million Vesting Shares were excluded from the calculation of basic and diluted per share calculations as the vesting thresholds have not yet been met as of the end of the reporting period.

Subsequent Events

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events[OPEN]

Basis of Presentation and Rec_2

Basis of Presentation and Recent Accounting Standards (Policies)	3 Months Ended
	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Recent Accounting Standards	Basis of Presentation and Recent Accounting Standards The accompanying unaudited condensed consolidated financial statements of the Company were prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial information and in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although the Company believes that the disclosures are adequate to make the information presented not misleading. Management believes the unaudited condensed consolidated financial statements for interim periods presented contain all necessary adjustments to state fairly, in all material respects, the Company's financial position, results of operations and cash flows for the interim periods presented. Operating results for the three months ended March 31, 2022 are not necessarily indicative of the results the Company expects for the entire year. In addition, the influence of seasonality, changes in payor contracts, changes in rate per visit, changes in referral and visit volumes, strategic transactions, labor market dynamics and wage inflation, changes in laws and general economic conditions in the markets in which the Company operates and other factors impacting the Company's operations may result in any period not being comparable to the same period in previous years. Preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts during the reporting period. Actual results could differ from those estimates.
Segment reporting	The Company reports segment information based on the management approach. The management approach designates the internal reporting used by management for making decisions and assessing performance as the source of the Company’s reportable segments. All of the Company’s operations are conducted within the United States. Our chief operating decision maker (“CODM”) is our Chief Executive Officer, who reviews financial information presented on a consolidated basis for purposes of making decisions, assessing financial performance and allocating resources. We operate our business as one operating segment and therefore we have one reportable segment.
Recently adopted accounting guidance and Recent accounting pronouncements	Recently adopted accounting guidance 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 , which provides optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. This standard was subsequently amended by ASU No. 2021-01, Reference Rate Reform (Topic 848): Scope . This standard is optional and may be applied by entities after March 12, 2020, but no later than December 31, 2022. As of March 31, 2022, the Company has derivative instruments for which the interest rates are indexed to the London InterBank Offered Rate (“LIBOR”). During the period ended March 31, 2022, the Company modified the reference rate index on its hedged items from LIBOR to the Secured Overnight Financing Rate ("SOFR"). The Company elected to apply the hedge accounting expedients related to probability and the assessments of effectiveness for future cash flows to assume that the index upon which future hedged transactions will be based matches the index on the corresponding derivatives, which is LIBOR. The guidance allows for different expedient elections to be made at different points in time. As of March 31, 2022, the Company does not anticipate that this guidance will have a material impact on its consolidated financial statements, however, the Company will continue to assess the potential impact on its future hedging relationships and expedient elections, as applicable. Recent accounting pronouncements In October 2021, the FASB issued ASU 2021-08, Business Combinations (Topic 805): Accounting for Contract Assets and Liabilities from Contracts with Customers , which provides guidance to improve the accounting for acquired revenue contracts with customers in a business combination by addressing diversity in practice. This ASU is effective for the Company on January 1, 2023, with early adoption permitted, and shall be applied on a prospective basis to business combinations that occur on or after the adoption date. The Company is evaluating the effect that the implementation of this standard may have on the Company's consolidated financial statements, but does not currently expect the impact to be material. In November 2021, the FASB issued ASU 2021-10, Government Assistance (Topic 832): Disclosures by Business Entities about Government Assistance , which provides guidance to increase the transparency of government assistance transactions with business entities that are accounted for by applying a grant or contribution accounting model. This ASU is effective for the Company's annual financial statements to be issued for the year ended December 31, 2022, with early adoption permitted. The Company expects to adopt this new accounting standard in its Annual Report on Form 10-K for the year ended December 31, 2022, and does not expect the adoption of this standard to have a material impact on the Company's consolidated financial statements.
Leases	LeasesThe Company leases various facilities and office equipment for its physical therapy operations and administrative support functions under operating leases. The Company’s initial operating lease terms are generally between 7 and 10 years, and typically contain options to renew for varying terms. Right-of-use ("ROU") assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The amortization of operating lease ROU assets and the accretion of operating lease liabilities are reported together as fixed lease expense. The fixed lease expense is recognized on a straight-line basis over the life of the lease.

Business Combinations and Div_2

Business Combinations and Divestiture (Tables)	3 Months Ended
Business Combinations and Divestiture (Tables)	Mar. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Summary of Shares Issued and Flow of Funds Related to Business Combination	Immediately following the Business Combination, there were 207.3 million shares issued and 196.6 million outstanding shares of common stock of ATI Physical Therapy, Inc., consisting of the following (in thousands): Class A Common Shares FAII Class A common stock prior to Business Combination 34,500 FAII Class F common stock prior to Business Combination (1) 8,625 Less: FAII Class A common stock redemptions (8,988) FAII common shares (Class A and Class F) 34,137 Add: Shares issued to Wilco Holdco stockholders (2, 3) 130,300 Add: Shares issued through PIPE investment 30,000 Add: Shares issued to Wilco Holdco Series A Preferred stockholders 12,845 Total shares issued as of the Closing Date of the Business Combination (4) 207,282 Less: Vesting Shares (1) (8,625) Less: Restricted shares (3) (2,014) Total shares outstanding as of the Closing Date of the Business Combination (4) 196,643 (1) Per the Merger Agreement, as of the closing of the Business Combination, all Class F shares converted into the equivalent number of Class A common shares and became subject to certain vesting and forfeiture provisions ("Vesting Shares") as detailed in Note 13 - Contingent Common Shares Liability . (2) Includes 1.2 million unrestricted shares upon distribution to holders of vested ICUs under the Wilco Acquisition, LP 2016 Equity Incentive Plan. (3) Includes 2.0 million restricted shares upon distribution to holders of unvested ICUs under the Wilco Acquisition, LP 2016 Equity Incentive Plan. (4 ) Excludes 15.0 million Earnout Shares, 6.9 million Public Warrants and 3.0 million Private Placement Warrants to purchase Class A common stock. Refer to Note 12 - IPO Warrant Liability and Note 13 - Contingent Common Shares Liability for further details. The following table reflects the components of cash movement related to the Business Combination, PIPE investment and debt repayments (in thousands): Cash in trust with FAII as of the Closing Date of the Business Combination $ 345,036 Cash used for redemptions of FAII Class A common stock (89,877) FAII transaction costs paid at closing (25,821) Cash inflow from Business Combination 229,338 Wilco Holdco, Inc. transaction costs offset against proceeds (19,233) Net proceeds from FAII in Business Combination 210,105 Cash proceeds from PIPE investment 300,000 Repayment of second lien subordinated loan (231,335) Partial repayment of 2016 first lien term loan (216,700) Cash payment to Wilco Holdco Series A Preferred stockholders (59,000) Wilco Holdco, Inc. transaction costs expensed during 2021 (5,543) Net decrease in cash related to Business Combination, PIPE investment and debt repayments $ (2,473)

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
Revenue from Contracts with Customers (Tables)	Mar. 31, 2022
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Net Operating Revenue By Major Service Line and Associated Payor Class	The following table disaggregates net operating revenue by major service line for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Net patient revenue $ 138,925 $ 132,271 ATI Worksite Solutions (1) 8,651 8,493 Management Service Agreements (1) 3,155 3,497 Other revenue (1) 3,091 4,801 $ 153,822 $ 149,062 (1) ATI Worksite Solutions, Management Service Agreements and Other revenue are included within other revenue on the face of the condensed consolidated statements of operations. The following table disaggregates net patient revenue for each associated payor class as a percentage of total net patient revenue for the periods indicated below: Three Months Ended March 31, 2022 March 31, 2021 Commercial 56.8 % 55.4 % Government 23.6 % 22.6 % Workers’ compensation 13.2 % 16.0 % Other (1) 6.4 % 6.0 % 100.0 % 100.0 %

Goodwill, Trade Name and Othe_2

Goodwill, Trade Name and Other Intangible Assets (Tables)	3 Months Ended
Goodwill, Trade Name and Other Intangible Assets (Tables)	Mar. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in The Carrying Amount of Goodwill	Changes in the carrying amount of goodwill consisted of the following (in thousands): Total Goodwill Goodwill at December 31, 2021 (1) $ 608,811 Impairment charges (116,335) Acquisitions (2) (236) Goodwill at March 31, 2022 $ 492,240 (1) Net of accumulated impairment losses of $726.8 million. (2) Represents final valuation adjustments related to 2021 acquisitions. Refer to Note 3 - Business Combinations and Divestiture for additional information.
Schedule of Carrying Amounts of Indefinite-Lived Intangible Assets	The table below summarizes the Company’s carrying amount of trade name and other intangible assets at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Gross intangible assets: ATI trade name (1) $ 369,954 $ 409,360 Non-compete agreements 2,395 2,405 Other intangible assets 640 640 Accumulated amortization: Accumulated amortization – non-compete agreements (604) (425) Accumulated amortization – other intangible assets (295) (284) Total trade name and other intangible assets, net $ 372,090 $ 411,696 (1) Not subject to amortization. The Company recorded $39.4 million of impairment charges related to the trade name indefinite-lived intangible asset during the three months ended March 31, 2022.
Schedule of Carrying Amounts of Finite-Lived Intangible Assets	The table below summarizes the Company’s carrying amount of trade name and other intangible assets at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Gross intangible assets: ATI trade name (1) $ 369,954 $ 409,360 Non-compete agreements 2,395 2,405 Other intangible assets 640 640 Accumulated amortization: Accumulated amortization – non-compete agreements (604) (425) Accumulated amortization – other intangible assets (295) (284) Total trade name and other intangible assets, net $ 372,090 $ 411,696 (1) Not subject to amortization. The Company recorded $39.4 million of impairment charges related to the trade name indefinite-lived intangible asset during the three months ended March 31, 2022.

Property and Equipment (Tables)

Property and Equipment (Tables)	3 Months Ended
Property and Equipment (Tables)	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment and Depreciation Expense	Property and equipment consisted of the following at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Equipment $ 37,067 $ 36,278 Furniture and fixtures 17,300 17,141 Leasehold improvements 187,489 183,542 Automobiles 19 19 Computer equipment and software 95,855 95,362 Construction-in-progress 4,134 3,793 341,864 336,135 Accumulated depreciation and amortization (205,088) (196,405) Property and equipment, net $ 136,776 $ 139,730 The following table presents the amount of depreciation expense recorded in rent, clinic supplies, contract labor and other and selling, general and administrative expenses in the Company’s condensed consolidated statements of operations for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Rent, clinic supplies, contract labor and other $ 7,086 $ 6,506 Selling, general and administrative expenses 2,835 3,058 Total depreciation expense $ 9,921 $ 9,564

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	3 Months Ended
Accrued Expenses and Other Liabilities (Tables)	Mar. 31, 2022
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consisted of the following at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Salaries and related costs $ 17,174 $ 27,257 CARES Act funds (1) 13,910 18,179 Accrued professional fees 8,993 5,649 Credit balance due to patients and payors 4,049 4,240 Accrued interest 4,046 — Accrued contract labor 3,520 2,057 Transaction-related costs (2) 303 349 Other payables and accrued expenses 7,396 6,853 Total $ 59,391 $ 64,584 (1) Includes current portion of MAAPP funds received and deferred employer Social Security tax payments. (2) Represents costs related to public readiness initiatives and corporate transactions.

Borrowings (Tables)

Borrowings (Tables)	3 Months Ended
Borrowings (Tables)	Mar. 31, 2022
Debt Disclosure [Abstract]
Summary of Long-Term Debt	Long-term debt consisted of the following at March 31, 2022 and December 31, 2021 (in thousands): March 31, 2022 December 31, 2021 Senior Secured Term Loan (1) (due February 24, 2028) $ 500,000 $ — 2016 first lien term loan (2) — 555,048 Less: unamortized debt issuance costs (12,303) (1,935) Less: unamortized original issue discount (9,880) (1,147) Total debt, net 477,817 551,966 Less: current portion of long-term debt — (8,167) Long-term debt, net $ 477,817 $ 543,799 (1) Interest rate of 8.25% at March 31, 2022, with interest payable in designated installments at a variable interest rate. The effective interest rate for the Senior Secured Term Loan was 9.2% at March 31, 2022. (2) Loan balance was repaid in its entirety on February 24, 2022. The effective interest rate for the 2016 first lien term loan was 4.9% at December 31, 2021.
Schedule of Aggregate Maturities of Long-Term Debt	Aggregate maturities of long-term debt at March 31, 2022 are as follows (in thousands): 2022 (remainder of year) $ — 2023 — 2024 — 2025 — 2026 — Thereafter 500,000 Total future maturities 500,000 Unamortized original issue discount and debt issuance costs (22,183) Total debt, net $ 477,817

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
Share-Based Compensation (Tables)	Mar. 31, 2022
Share-based Payment Arrangement [Abstract]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The following weighted-average assumptions were used for the options granted in 2022: 2022 Weighted-average grant-date fair value of options $1.01 Risk-free interest rate 1.74% Term (years) 6.2 Volatility 61.20% Expected dividend —%

Mezzanine and Stockholders' E_2

Mezzanine and Stockholders' Equity (Tables)	3 Months Ended
Mezzanine and Stockholders' Equity (Tables)	Mar. 31, 2022
Equity [Abstract]
Schedule of Temporary Equity	The following table reflects the components of proceeds related to the Series A Senior Preferred Stock (in thousands): Gross proceeds allocated to Series A Senior Preferred Stock $ 144,667 Less: original issue discount (1,447) Less: issuance costs (2,880) Net proceeds received from issuance of Series A Senior Preferred Stock $ 140,340 The following table presents the change in the aggregate stated value and stated value per share of the Series A Senior Preferred Stock since the Refinancing Date (in thousands, except per share data): Series A Senior Preferred Stock Aggregate stated value as of February 24, 2022 $ 165,000 Accumulated paid in-kind dividends as of March 31, 2022 1,925 Aggregate stated value as of March 31, 2022 $ 166,925 Preferred shares issued and outstanding as of March 31, 2022 165 Stated value per share as of March 31, 2022 $ 1,011.67
Schedule of Components Of Proceeds Related to Warrants	The following table reflects the components of proceeds related to the 2022 Warrants (in thousands): Series I Warrants Series II Warrants Total Gross proceeds allocated to 2022 Warrants $ 5,101 $ 15,232 $ 20,333 Less: original issue discount (51) (152) (203) Less: issuance costs (102) (303) (405) Net proceeds received from issuance of 2022 Warrants $ 4,948 $ 14,777 $ 19,725
Schedule of Shares of Class A Common Stock Reserved for Potential Future Issuance	As of March 31, 2022, shares of Class A common stock reserved for potential future issuance, on an as-if converted basis, were as follows (in thousands): March 31, 2022 Shares available for grant under the ATI 2021 Equity Incentive Plan 9,395 Earnout Shares reserved 15,000 2022 Warrants outstanding 11,498 IPO Warrants outstanding 9,867 Vesting Shares reserved (1) 8,625 Restricted shares (1,2) 1,248 Total shares of common stock reserved 55,633 (1) Represents shares of Class A common stock legally issued, but not outstanding, as of March 31, 2022. (2) Represents a portion of the 2.0 million restricted shares distributed following the Business Combination to holders of unvested Incentive Common Units under the Wilco Acquisition, LP 2016 Equity Incentive Plan.

IPO Warrant Liability (Tables)

IPO Warrant Liability (Tables)	3 Months Ended
IPO Warrant Liability (Tables)	Mar. 31, 2022
Other Liabilities Disclosure [Abstract]
Summary of Warrant Liability	The following table presents the change in the fair value of Private Placement Warrants that is recognized in change in fair value of warrant liability in the condensed consolidated statement of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 1,305 Changes in fair value (504) Fair value, end of period $ 801 The following table presents the changes in the fair value of the Public Warrants that is recognized in change in fair value of warrant liability in the condensed consolidated statements of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 3,036 Changes in fair value (1,173) Fair value, end of period $ 1,863

Contingent Common Shares Liab_2

Contingent Common Shares Liability (Tables)	3 Months Ended
Contingent Common Shares Liability (Tables)	Mar. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Change in Fair Value of Earn Out Shares	The following table presents the changes in the fair value of the Earnout Shares that is recognized in change in fair value of contingent common shares liability in the condensed consolidated statements of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 28,800 Changes in fair value (15,450) Fair value, end of period $ 13,350 Refer to Note 14 - Fair Value Measurements for further details. The following table presents the changes in the fair value of the Vesting Shares that is recognized in change in fair value of contingent common shares liability in the condensed consolidated statements of operations for the period ending March 31, 2022 (in thousands): Three Months Ended March 31, 2022 Fair value, beginning of period $ 16,560 Changes in fair value (8,884) Fair value, end of period $ 7,676 Refer to Note 14 - Fair Value Measurements for further details.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
Fair Value Measurements (Tables)	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Key Fair Value Measurement Inputs	The key inputs into the Monte Carlo option pricing model were as follows as of March 31, 2022 and December 31, 2021 for the respective Level 3 instruments : Earnout Shares Vesting Shares March 31, 2022 December 31, 2021 March 31, 2022 December 31, 2021 Risk-free interest rate 2.33% 1.50% 2.33% 1.50% Volatility 50.82% 44.86% 50.82% 44.86% Dividend yield —% —% —% —% Expected term (years) 9.2 9.5 9.2 9.5 Share price $1.88 $3.39 $1.88 $3.39

Leases (Tables)

Leases (Tables)	3 Months Ended
Leases (Tables)	Mar. 31, 2022
Leases [Abstract]
Schedule of Lease Cost, Supplemental Cash Flow, and Other Information Related to Leases	Lease costs incurred by lease type were as follows for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Lease cost Operating lease cost $ 16,703 $ 15,823 Variable lease cost (1) 5,205 4,936 Total lease cost (2) $ 21,908 $ 20,759 (1) Includes short term lease costs, which are immaterial . (2) Sublease income was immaterial . Other supplemental quantitative disclosures were as follows for the periods indicated below (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 16,438 $ 16,166 Cash payments related to lease terminations $ — $ 4,570 Right-of-use assets obtained in exchange for new operating lease liabilities $ 5,142 $ 5,399 Average lease terms and discount rates as of March 31, 2022 and December 31, 2021 were as follows: March 31, 2022 December 31, 2021 Weighted-average remaining lease term: Operating leases 6.3 years 6.4 years Weighted-average discount rate: Operating leases 6.5% 6.5%
Schedule of Estimated Undiscounted Future Lease Payments	Estimated undiscounted future lease payments under non-cancellable operating leases, along with a reconciliation of the undiscounted cash flows to operating lease liabilities, respectively, at March 31, 2022 were as follows (in thousands): Year 2022 (remainder of year after March 31, 2022) $ 50,865 2023 66,781 2024 59,498 2025 50,358 2026 44,009 Thereafter 97,574 Total undiscounted future cash flows 369,085 Less: Imputed Interest (70,080) Present value of future cash flows $ 299,005 Presentation on Balance Sheet Current $ 50,651 Non-current $ 248,354

Loss per Share (Tables)

Loss per Share (Tables)	3 Months Ended
Loss per Share (Tables)	Mar. 31, 2022
Earnings Per Share [Abstract]
Schedule of Calculation of Both Basic and Diluted Loss Per Share	The calculation of both basic and diluted loss per share for the periods indicated below was as follows (in thousands, except per share data): Three Months Ended March 31, 2022 March 31, 2021 Basic and diluted loss per share: Net loss $ (138,223) $ (17,818) Less: Net (loss) income attributable to non-controlling interests (473) 1,309 Less: Series A Senior Preferred cumulative dividend 1,925 — Loss available to common stockholders $ (139,675) $ (19,127) Weighted average shares outstanding (1,2) 199,971 128,286 Basic and diluted loss per share $ (0.70) $ (0.15) (1) The weighted-average number of shares outstanding in periods presented prior to the closing of the Business Combination has been retrospectively adjusted based on the exchange ratio established through the transaction. (2) Included within weighted average shares outstanding following the 2022 Debt Refinancing are common shares issuable upon the exercise of the Series II Warrants, as the Series II Warrants are exercisable at any time for nominal consideration. As such, the shares are considered to be outstanding for the purpose of calculating basic and diluted loss per share.
Schedule of Antidilutive Securities Excluded From Computation of Diluted Shares Outstanding	For the periods presented, the following securities were not required to be included in the computation of diluted shares outstanding, as their impact would have been anti-dilutive. Figures presented are based on the number of underlying Class A common shares following the Business Combination (in thousands): Three Months Ended March 31, 2022 March 31, 2021 Series I Warrants 5,226 — IPO Warrants 9,867 — Restricted shares (1) 1,248 — Stock options 5,951 — RSUs 4,886 — RSAs 366 — Total 27,544 — (1) Represents a portion of the 2.0 million restricted shares distributed following the Business Combination to holders of unvested Incentive Common Units under the Wilco Acquisition, LP 2016 Equity Incentive Plan.

Overview of the Company (Detail

Overview of the Company (Details) $ in Thousands	3 Months Ended
Overview of the Company (Details) $ in Thousands	Mar. 31, 2022USD ($)clinicstate	Jun. 30, 2020USD ($)	Dec. 31, 2021USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of stores \| clinic	922
Number of stores under management service agreements \| clinic	20
Number of states in which entity operates \| state	25
Unusual or Infrequent Item, or Both [Line Items]
Accrued expenses and other liabilities	$ 59,391		$ 64,584
CARES Act, MAAPP Funds
Unusual or Infrequent Item, or Both [Line Items]
General distributions received		$ 26,700
Proceeds from sale of Home Health service line	4,300
Accrued expenses and other liabilities	8,000		12,300
Government Assistance, CARES Act, Deferral Of Employer Portion Of Social Security Taxes
Unusual or Infrequent Item, or Both [Line Items]
Accrued expenses and other liabilities	$ 5,900		$ 5,900

Basis of Presentation and Rec_3

Basis of Presentation and Recent Accounting Standards (Details)	3 Months Ended
	Mar. 31, 2022segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1
Number of reportable segments	1

Business Combinations and Div_3

Business Combinations and Divestiture - Narrative (Details) $ / shares in Units, $ in Thousands	Jun. 16, 2021USD ($)$ / sharesshares	Dec. 31, 2021USD ($)centerclinic$ / sharesshares	Mar. 31, 2022USD ($)$ / sharesshares	Oct. 01, 2021USD ($)	Jun. 15, 2021shares
Schedule Of Reverse Recapitalization [Line Items]
Shares issued to Wilco Holdco stockholders (in shares)	130,300,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.01	$ 0.0001	$ 0.0001
Exchange ratio	136.7
Common stock, shares Issued (in shares)	207,282,000	207,400,000	207,400,000
Common stock, shares outstanding (in shares)	196,643,000	197,400,000	197,500,000
Transaction cost \| $		$ 5,543
Transaction cost off-set against additional paid-in capital \| $		19,200
Goodwill, net \| $		$ 608,811	$ 492,240
Three Acquisitions 2021
Schedule Of Reverse Recapitalization [Line Items]
Number of businesses acquired \| center		3
Number of clinics \| clinic		7
Cash consideration \| $		$ 4,500
Contingent consideration liability \| $		1,400
Goodwill, net \| $		$ 5,500
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Home Health service line
Schedule Of Reverse Recapitalization [Line Items]
Sale price \| $				$ 7,300
Public Warrant
Schedule Of Reverse Recapitalization [Line Items]
Number of shares called by each warrant	6,900,000		6,900,000
Private Placement Warrant
Schedule Of Reverse Recapitalization [Line Items]
Number of shares called by each warrant	3,000,000		3,000,000
Warrants transferred and surrender in conjunction with business combination (in shares)	3,000,000
Earnout Shares
Schedule Of Reverse Recapitalization [Line Items]
Contingent common share liability (in shares, up to)	15,000,000
Contingent common share liability term	10 years
2016 Plan
Schedule Of Reverse Recapitalization [Line Items]
Unrestricted shares ( in shares)	1,200,000
Wilco Holdco, Inc.
Schedule Of Reverse Recapitalization [Line Items]
Common stock, par value (in dollars per share) \| $ / shares	$ 0.01
Class A Common Stock
Schedule Of Reverse Recapitalization [Line Items]
Shares issued to Wilco Holdco stockholders (in shares)	130,300,000
Shares issued to Wilco Holdco stockholders, value per share (in dollars per share) \| $ / shares	$ 0.0001
Common stock, par value (in dollars per share) \| $ / shares			$ 0.0001
Unrestricted shares ( in shares)	128,300,000
Common stock, shares Issued (in shares)			207,400,000
Common stock, shares outstanding (in shares)			197,500,000
Number of shares issued as consideration	30,000,000
Price per share (in dollars per share) \| $ / shares	$ 10
Aggregate purchase price \| $	$ 300,000
Equity consideration transferred in exchange for redemption of preferred stock \| $	$ 59,000
Equity consideration transferred in exchange for redemption of preferred stock (in shares)	12,800,000
Class A Common Stock \| FAII
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)					34,500,000
Class A Common Stock \| Fortress
Schedule Of Reverse Recapitalization [Line Items]
Number of shares issued as consideration	7,500,000
Price per share (in dollars per share) \| $ / shares	$ 10
Aggregate purchase price \| $	$ 75,000
Class A Common Stock \| 2016 Plan
Schedule Of Reverse Recapitalization [Line Items]
Restricted shares (in shares)	2,000,000
Class F Common Stock \| FAII
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)					8,625,000

Business Combinations and Div_4

Business Combinations and Divestiture - Summary of Shares Issued and Outstanding (Details) - shares shares in Thousands	Jun. 16, 2021	Mar. 31, 2022	Dec. 31, 2021	Jun. 15, 2021
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)	196,643	197,500	197,400
FAII common shares (Class A and Class F)	34,137
Add: Shares issued to Wilco Holdco stockholders (in shares)	130,300
Add: Shares issued through PIPE investment (in shares)	30,000
Add: Shares issued to Wilco Holdco Series A Preferred stockholders (in shares)	12,845
Common stock, shares Issued (in shares)	207,282	207,400	207,400
Less: Vesting Shares	(8,625)
Less: Restricted shares	(2,014)
Common stock, shares outstanding (in shares)	196,643	197,500	197,400
Public Warrant
Schedule Of Reverse Recapitalization [Line Items]
Number of shares called by each warrant	6,900	6,900
Private Placement Warrant
Schedule Of Reverse Recapitalization [Line Items]
Number of shares called by each warrant	3,000	3,000
2016 Plan
Schedule Of Reverse Recapitalization [Line Items]
Unrestricted shares (in shares)	1,200
Class A Common Stock
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)		197,500
Add: Shares issued to Wilco Holdco stockholders (in shares)	130,300
Common stock, shares Issued (in shares)		207,400
Common stock, shares outstanding (in shares)		197,500
Unrestricted shares (in shares)	128,300
Class A Common Stock \| 2016 Plan
Schedule Of Reverse Recapitalization [Line Items]
Restricted shares (in shares)	2,000
Class A Common Stock \| FAII
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)				34,500
Less: FAII Class A common stock redemptions (in shares)	(8,988)
Common stock, shares outstanding (in shares)				34,500
Class F Common Stock \| FAII
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)				8,625
Common stock, shares outstanding (in shares)				8,625

Business Combinations and Div_5

Business Combinations and Divestiture - Flow of Funds (Details) - USD ($) $ in Thousands	Jun. 16, 2021	Dec. 31, 2021
Schedule Of Reverse Recapitalization [Line Items]
Cash in trust with FAII as of the Closing Date of the Business Combination	$ 345,036
Cash used for redemptions of FAII Class A common stock	(89,877)
FAII transaction costs paid at closing	(25,821)
Cash inflow from Business Combination	229,338
Wilco Holdco, Inc. transaction costs offset against proceeds	(19,233)
Net proceeds from FAII in Business Combination	210,105
Cash proceeds from PIPE investment	300,000
Cash payment to Wilco Holdco Series A Preferred stockholders	(59,000)
Wilco Holdco, Inc. transaction costs expensed during 2021		$ (5,543)
Net decrease in cash related to Business Combination, PIPE investment and debt repayments		$ (2,473)
Second Lien Subordinated Loan
Schedule Of Reverse Recapitalization [Line Items]
Repayments of debt	(231,335)
2016 First lien Term Loan
Schedule Of Reverse Recapitalization [Line Items]
Repayments of debt	$ (216,700)

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Net operating revenue	$ 153,822	$ 149,062
Net patient revenue
Disaggregation of Revenue [Line Items]
Net operating revenue	$ 138,925	$ 132,271
Net operating revenue (as percent)	100.00%	100.00%
Net patient revenue \| Commercial
Disaggregation of Revenue [Line Items]
Net operating revenue (as percent)	56.80%	55.40%
Net patient revenue \| Government
Disaggregation of Revenue [Line Items]
Net operating revenue (as percent)	23.60%	22.60%
Net patient revenue \| Workers’ compensation
Disaggregation of Revenue [Line Items]
Net operating revenue (as percent)	13.20%	16.00%
Net patient revenue \| Other
Disaggregation of Revenue [Line Items]
Net operating revenue (as percent)	6.40%	6.00%
ATI Worksite Solutions
Disaggregation of Revenue [Line Items]
Net operating revenue	$ 8,651	$ 8,493
Management Service Agreements
Disaggregation of Revenue [Line Items]
Net operating revenue	3,155	3,497
Other revenue
Disaggregation of Revenue [Line Items]
Net operating revenue	$ 3,091	$ 4,801

Goodwill, Trade Name and Othe_3

Goodwill, Trade Name and Other Intangible Assets - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 608,811
Impairment charges	(116,335)
Acquisitions	(236)
Goodwill, Ending Balance	$ 492,240
Accumulated goodwill impairment loss		$ 726,800

Goodwill, Trade Name and Othe_4

Goodwill, Trade Name and Other Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Trade name and other intangible assets, net	$ 372,090	$ 411,696
ATI trade name
Indefinite-lived Intangible Assets [Line Items]
Gross intangible assets	369,954	409,360
Impairment of indefinite lived intangible assets	39,400
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	2,395	2,405
Accumulated amortization:	(604)	(425)
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	640	640
Accumulated amortization:	$ (295)	$ (284)

Goodwill, Trade Name and Othe_5

Goodwill, Trade Name and Other Intangible Assets - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022USD ($)
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment loss	$ 116,335
ATI trade name
Indefinite-lived Intangible Assets [Line Items]
Impairment of indefinite lived intangible assets	$ 39,400

Property and Equipment - Carryi

Property and Equipment - Carrying Amount (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 341,864	$ 336,135
Accumulated depreciation and amortization	(205,088)	(196,405)
Property and equipment, net	136,776	139,730
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	37,067	36,278
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	17,300	17,141
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	187,489	183,542
Automobiles
Property, Plant and Equipment [Line Items]
Property and equipment, gross	19	19
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	95,855	95,362
Construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,134	$ 3,793

Property and Equipment - Deprec

Property and Equipment - Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Property, Plant and Equipment [Line Items]
Total depreciation expense	$ 9,921	$ 9,564
Rent, clinic supplies, contract labor and other
Property, Plant and Equipment [Line Items]
Total depreciation expense	7,086	6,506
Selling, general and administrative expenses
Property, Plant and Equipment [Line Items]
Total depreciation expense	$ 2,835	$ 3,058

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Salaries and related costs	$ 17,174	$ 27,257
CARES Act funds	13,910	18,179
Accrued professional fees	8,993	5,649
Credit balance due to patients and payors	4,049	4,240
Accrued interest	4,046	0
Accrued contract labor	3,520	2,057
Transaction-related costs	303	349
Other payables and accrued expenses	7,396	6,853
Accrued expenses and other liabilities	$ 59,391	$ 64,584

Borrowings - Long-term debt (De

Borrowings - Long-term debt (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total future maturities	$ 500,000
Less: unamortized debt issuance costs	(12,303)	$ (1,935)
Less: unamortized original issue discount	(9,880)	(1,147)
Total debt, net	477,817	551,966
Less: current portion of long-term debt	0	(8,167)
Long-term debt, net	477,817	$ 543,799
2016 First lien Term Loan
Debt Instrument [Line Items]
Effective interest rate (in percent)		4.90%
2016 First lien Term Loan \| Secured Debt
Debt Instrument [Line Items]
Total future maturities	$ 0	$ 555,048
Senior Secured Term Loan
Debt Instrument [Line Items]
State interest rate (in percent)	8.25%
Effective interest rate (in percent)	9.20%
Senior Secured Term Loan \| Secured Debt
Debt Instrument [Line Items]
Total future maturities	$ 500,000	$ 0

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - USD ($)	Feb. 24, 2022	Jun. 16, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Debt Instrument [Line Items]
Principal payments on long-term debt			$ 555,048,000	$ 2,042,000
Loss on extinguishment of debt			2,809,000	$ 0
Warrants purchase common stock aggregate stated value	$ 165,000,000
Balance of unamortized issuance costs			12,303,000		$ 1,935,000
2016 First lien Term Loan
Debt Instrument [Line Items]
Principal payments on long-term debt	555,000,000	$ 216,700,000
Loss on extinguishment of debt	2,800,000	1,700,000
Second Lien Subordinated Loan
Debt Instrument [Line Items]
Principal payments on long-term debt		231,300,000
Loss on extinguishment of debt		$ 3,800,000
2022 Credit Agreement
Debt Instrument [Line Items]
Debt amount	550,000,000
Debt issuance costs, gross	12,500,000
Original issuance discount	10,000,000
Minimum liquidity amount	30,000,000
Prepayment upon insurance proceeds in excess of	$ 15,000,000
2022 Credit Agreement \| Beginning in the second quarter of 2024
Debt Instrument [Line Items]
Maximum debt to EBITDA ratio allowed	7
2022 Credit Agreement \| In third quarter of 2024
Debt Instrument [Line Items]
Maximum debt to EBITDA ratio allowed	6.75
2022 Credit Agreement \| First quarter of 2025
Debt Instrument [Line Items]
Maximum debt to EBITDA ratio allowed	6.25
2022 Credit Agreement \| Secured Debt
Debt Instrument [Line Items]
Debt amount	$ 500,000,000
Interest in-kind interest to pay	2.00%
Premium rate	0.50%
2022 Credit Agreement \| Secured Debt \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Floor rate (as a percent)	1.00%
Basis spread on variable rate (as a percent)	7.25%
2022 Credit Agreement \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, commitment fee percentage	0.50%
2022 Credit Agreement \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50,000,000
Debt issuance costs, gross	500,000
Balance of unamortized issuance costs			700,000
2022 Credit Agreement \| Letter of Credit \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	10,000,000
Letters of credit outstanding			$ 1,200,000		1,200,000
First lien credit agreement \| Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Debt issuance costs, gross	$ 200,000
Balance of unamortized issuance costs					$ 300,000

Borrowings - Maturities (Detail

Borrowings - Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
2022 (remainder of year)	$ 0
2023	0
2024	0
2025	0
2026	0
Thereafter	500,000
Total future maturities	500,000
Unamortized original issue discount and debt issuance costs	(22,183)
Total debt, net	$ 477,817	$ 551,966

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved	55,633,000
Share-based compensation	$ 1,960	$ 504
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issued (in usd per share)	$ 2.23
2021 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance ( in shares)	20,700,000
Total shares of common stock reserved	9,400,000
Stock options granted (in shares)	5,200,000
Weighted-average grant-date fair value of options ( in dollar per share)	$ 1.01
Share-based payment arrangement, nonvested award, option, cost not yet recognized, amount	$ 6,200
Share-based compensation	$ 2,000
2021 Plan \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted in period (in shares)	4,500,000
Share-based payment arrangement, nonvested award, option, cost not yet recognized, amount	$ 9,800
Period of recognition	2 years 6 months
2021 Plan \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of recognition	3 years 7 months 6 days

Share-Based Compensation - Valu

Share-Based Compensation - Valuation Assumption (Details) - 2021 Plan	3 Months Ended
	Mar. 31, 2022$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of options ( in dollar per share)	$ 1.01
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.74%
Term (years)	6 years 2 months 12 days
Volatility	61.20%
Expected dividend	0.00%

Mezzanine and Stockholders' E_3

Mezzanine and Stockholders' Equity - Narrative (Details)	Feb. 24, 2022USD ($)$ / sharesshares	Jun. 16, 2021$ / sharesshares	Mar. 31, 2022USD ($)vote$ / sharesshares	Mar. 31, 2021USD ($)	Dec. 31, 2021USD ($)$ / sharesshares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)			200,000		0
Exercise price of warrant (in dollars per share) \| $ / shares			$ 11.50
Preferred stock, par value (dollars per share) \| $ / shares			$ 0.0001		$ 0.0001
Warrants purchase common stock aggregate stated value \| $	$ 165,000,000
Preferred stock, shares authorized (in shares)			1,000,000		1,000,000
Preferred stock, shares outstanding (in shares)			200,000		0
Proceeds from issuance of Series A Senior Preferred Stock \| $			$ 144,667,000	$ 0
Proceeds from issuance of warrants \| $	$ 20,333,000		$ 20,333,000	$ 0
Common stock, shares authorized (in shares)			470,000,000		470,000,000
Common stock, par value (in dollars per share) \| $ / shares		$ 0.01	$ 0.0001		$ 0.0001
Common stock, shares Issued (in shares)		207,282,000	207,400,000		207,400,000
Common stock, shares outstanding (in shares)		196,643,000	197,500,000		197,400,000
Shares issued to Wilco Holdco stockholders (in shares)		130,300,000
Exchange ratio		136.7
Tax withholdings related to net share settlement of restricted stock awards (in shares)			10,000
Treasury stock (in shares)			40,000		30,000
Treasury stock, value \| $			$ 117,000		$ 95,000
2016 Plan
Class of Stock [Line Items]
Unrestricted shares ( in shares)		1,200,000
Series I Warrants
Class of Stock [Line Items]
Number of outstanding warrants (in shares)	5,200,000
Exercise price of warrant (in dollars per share) \| $ / shares	$ 3
Proceeds from issuance of warrants \| $	$ 5,101,000
Issuance discount \| $	$ 200,000
Series II Warrants
Class of Stock [Line Items]
Number of outstanding warrants (in shares)	6,300,000
Exercise price of warrant (in dollars per share) \| $ / shares	$ 0.01
Proceeds from issuance of warrants \| $	$ 15,232,000
Issuance discount \| $	$ 500,000
Series A Preferred
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)	165,000		165,000
Preferred stock, par value (dollars per share) \| $ / shares	$ 0.0001
Preferred tock, stated value (dollars per share) \| $ / shares	$ 1,000		$ 1,011.67
Preferred stock, shares authorized (in shares)	1,000,000
Preferred stock, shares outstanding (in shares)			165,000
Proceeds from issuance of Series A Senior Preferred Stock \| $	$ 144,667,000
Preferred stock, discount on shares \| $	2,900,000
Issuance discount \| $	$ 1,447,000
Annual dividend rate	12.00%
Discount on dividends	1.00%
In-kind increasing percentage	1.00%
Dividend rate, occurrence, increase percent	2.00%
Dividends, preferred stock, paid-in-kind \| $			$ 1,900,000
Redemption value \| $	$ 165,000,000		$ 166,925,000
Change in voting rights, ADBITDA threshold \| $	$ 100,000,000
Change in voting rights, change in ownership percent	50.10%
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)			470,000,000
Common stock, par value (in dollars per share) \| $ / shares			$ 0.0001
Common stock voting rights \| vote			1
Common stock, shares Issued (in shares)			207,400,000
Common stock, shares outstanding (in shares)			197,500,000
Shares issued to Wilco Holdco stockholders (in shares)		130,300,000
Shares issued to Wilco Holdco stockholders, value per share (in dollars per share) \| $ / shares		$ 0.0001
Unrestricted shares ( in shares)		128,300,000
Class A Common Stock \| 2016 Plan
Class of Stock [Line Items]
Restricted shares (in shares)		2,000,000
Class A Common Stock \| Series I Warrants
Class of Stock [Line Items]
Exercise period	5 years
Class A Common Stock \| Series II Warrants
Class of Stock [Line Items]
Exercise period	5 years

Mezzanine and Stockholders' E_4

Mezzanine and Stockholders' Equity - Components of Proceeds Related to the Series A Senior Preferred Stock (Details) - USD ($) $ in Thousands	Feb. 24, 2022	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Gross proceeds allocated to Series A Senior Preferred Stock		$ 144,667	$ 0
Series A Preferred
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Gross proceeds allocated to Series A Senior Preferred Stock	$ 144,667
Less: original issue discount	(1,447)
Less: issuance costs	(2,880)
Net proceeds received from issuance of Series A Senior Preferred Stock	$ 140,340

Mezzanine and Stockholders' E_5

Mezzanine and Stockholders' Equity - Aggregate Stated Value Of Series A Senior Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Mar. 31, 2022	Feb. 24, 2022	Dec. 31, 2021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares outstanding (in shares)	200,000		0
Preferred stock, shares issued (in shares)	200,000		0
Series A Preferred
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Aggregate stated value as of February 24, 2022	$ 165,000
Accumulated paid in-kind dividends	1,925
Aggregate stated value as of March 31, 2022	$ 166,925
Preferred stock, shares outstanding (in shares)	165,000
Preferred stock, shares issued (in shares)	165,000	165,000
Preferred tock, stated value (dollars per share)	$ 1,011.67	$ 1,000

Mezzanine and Stockholders' E_6

Mezzanine and Stockholders' Equity - Components of Proceeds Related to the Warrants (Details) - USD ($) $ in Thousands	Feb. 24, 2022	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of 2022 Warrants	$ 20,333	$ 20,333	$ 0
Original issue discount	(203)
Less: issuance costs	(405)
Issuance of 2022 Warrants	19,725	$ 19,725
Series I Warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of 2022 Warrants	5,101
Original issue discount	(51)
Less: issuance costs	(102)
Issuance of 2022 Warrants	4,948
Series II Warrants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of 2022 Warrants	15,232
Original issue discount	(152)
Less: issuance costs	(303)
Issuance of 2022 Warrants	$ 14,777

Mezzanine and Stockholders' E_7

Mezzanine and Stockholders' Equity - Reserved Shares (Details) - shares shares in Thousands	Jun. 16, 2021	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		55,633
Shares available for grant under the ATI 2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		9,395
Earnout Shares reserved
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		15,000
2022 Warrants outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		11,498
IPO Warrants outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		9,867
Vesting Shares reserved
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		8,625
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved		1,248
2016 Plan \| Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares (in shares)	2,000

Wilco Holdco Redeemable Prefe_2

Wilco Holdco Redeemable Preferred Stock (Details) - USD ($) $ in Thousands, shares in Millions	May 10, 2016	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Jun. 16, 2021
Class of Stock [Line Items]
Proceeds from issuance of Series A Senior Preferred Stock		$ 144,667	$ 0
Loss on settlement of redeemable preferred stock				$ 14,000
Class A Common Stock
Class of Stock [Line Items]
Equity consideration transferred in exchange for redemption of preferred stock					$ 59,000
Equity consideration transferred in exchange for redemption of preferred stock (in shares)					12.8
Wilco Holdco, Inc.
Class of Stock [Line Items]
Proceeds from issuance of Series A Senior Preferred Stock	$ 98,000
Annual dividend rate	10.25%
Quarterly increase in dividend rate after second anniversary	0.25%
Cumulative preferred dividends			$ 5,300

IPO Warrant Liability - Narrati

IPO Warrant Liability - Narrative (Details) - shares shares in Millions	Mar. 31, 2022	Jun. 16, 2021
Public Warrant
Class of Warrant or Right [Line Items]
Number of shares called by each warrant	6.9	6.9
Private Placement Warrant
Class of Warrant or Right [Line Items]
Number of shares called by each warrant	3	3

IPO Warrant Liability - Warrant

IPO Warrant Liability - Warrant Liability (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 4,341
Change in fair value of warrant liability	1,677	$ 0
Fair value, end of period	2,664
Private Placement Warrant
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,305
Change in fair value of warrant liability	(504)
Fair value, end of period	801
Public Warrant
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	3,036
Change in fair value of warrant liability	(1,173)
Fair value, end of period	$ 1,863

Contingent Common Shares Liab_3

Contingent Common Shares Liability - Narrative (Details)	Jun. 16, 2021tranche$ / sharesshares
Earnout Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	15,000,000
Contingent common share liability term	10 years
Number of tranches \| tranche	3
First Issuance, Earnout Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	5,000,000
First Issuance, Earnout Shares \| Weighted Average
Derivative [Line Items]
Stock price trigger (in dollars per share) \| $ / shares	$ 12
Second Issuance, Earnout Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	5,000,000
Second Issuance, Earnout Shares \| Weighted Average
Derivative [Line Items]
Stock price trigger (in dollars per share) \| $ / shares	$ 14
Third Issuance, Earnout Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	5,000,000
Third Issuance, Earnout Shares \| Weighted Average
Derivative [Line Items]
Stock price trigger (in dollars per share) \| $ / shares	$ 16
Vesting Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	8,600,000
Number of tranches \| tranche	3
First Issuance, Vesting Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	2,900,000
First Issuance, Vesting Shares \| Weighted Average
Derivative [Line Items]
Stock price trigger (in dollars per share) \| $ / shares	$ 12
Third Issuance, Vesting Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	2,900,000
Third Issuance, Vesting Shares \| Weighted Average
Derivative [Line Items]
Stock price trigger (in dollars per share) \| $ / shares	$ 16
Second Issuance, Vesting Shares
Derivative [Line Items]
Contingent consideration liability (in shares)	2,900,000
Second Issuance, Vesting Shares \| Weighted Average
Derivative [Line Items]
Stock price trigger (in dollars per share) \| $ / shares	$ 14

Contingent Common Shares Liab_4

Contingent Common Shares Liability - Derivatives and Fair Value (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022USD ($)
Schedule of Changes in Fair Value
Fair value, beginning of period	$ 45,360
Fair value, end of period	21,026
Earnout Shares
Schedule of Changes in Fair Value
Fair value, beginning of period	28,800
Changes in fair value	(15,450)
Fair value, end of period	13,350
Vesting Shares
Schedule of Changes in Fair Value
Fair value, beginning of period	16,560
Changes in fair value	(8,884)
Fair value, end of period	$ 7,676

Fair Value Measurements - Measu

Fair Value Measurements - Measurement Inputs (Details) - Fair Value, Inputs, Level 3	Mar. 31, 2022$ / shares	Dec. 31, 2021$ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Earnout Shares	0.0233	0.0150
Vesting Shares	0.0233	0.0150
Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Earnout Shares	0.5082	0.4486
Vesting Shares	0.5082	0.4486
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Earnout Shares	0	0
Vesting Shares	0	0
Expected term (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Earnout Share, Term	9 years 2 months 12 days	9 years 6 months
Vesting Shares, Term	9 years 2 months 12 days	9 years 6 months
Share price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Earnout Shares	1.88	3.39
Vesting Shares	1.88	3.39

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Effect income tax rate (in percent)	14.40%	37.10%
Income tax benefit	$ (23,281)	$ (10,515)

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Leases - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2022	Mar. 31, 2021
Lessee, Lease, Description [Line Items]
Operating lease assets additions	$ 5.7	$ 3.8
Operating lease liabilities, additions	$ 5.7	$ 3.8
Minimum
Lessee, Lease, Description [Line Items]
Initial operating lease term	7 years
Maximum
Lessee, Lease, Description [Line Items]
Initial operating lease term	10 years

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended
Leases - Lease Cost (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Leases [Abstract]
Operating lease cost	$ 16,703	$ 15,823
Variable lease cost	5,205	4,936
Total lease cost	$ 21,908	$ 20,759

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 16,438	$ 16,166
Cash payments related to lease terminations	0	4,570
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 5,142	$ 5,399

Leases - Other Information (Det

Leases - Other Information (Details)	Mar. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Weighted-average remaining lease term: Operating leases	6 years 3 months 18 days	6 years 4 months 24 days
Weighted-average discount rate: Operating leases	650.00%	650.00%

Leases - Maturity (Details)

Leases - Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Leases [Abstract]
2022 (remainder of year after March 31, 2022)	$ 50,865
2023	66,781
2024	59,498
2025	50,358
2026	44,009
Thereafter	97,574
Total undiscounted future cash flows	369,085
Less: Imputed Interest	(70,080)
Present value of future cash flows	299,005
Presentation on Balance Sheet
Current	50,651	$ 49,433
Non-current	$ 248,354	$ 250,597

Commitments and Contingencies (

Commitments and Contingencies (Details)	Aug. 16, 2021plaintiff
ATI Shareholders vs ATI Individual Defendants
Loss Contingencies [Line Items]
Number of plaintiffs	2

Loss per Share - Loss per Share

Loss per Share - Loss per Share Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Basic and diluted loss per share:
Net loss	$ (138,223)	$ (17,818)
Less: Net (loss) income attributable to non-controlling interests	(473)	1,309
Less: Series A Senior Preferred cumulative dividend	1,925	0
Loss available to common stockholders, basic	(139,675)	(19,127)
Loss available to common stockholders, diluted	$ (139,675)	$ (19,127)
Weighted average shares outstanding, basic (in shares)	199,971	128,286
Weighted average shares outstanding, diluted (in shares)	199,971	128,286
Basic loss (in dollars per share)	$ (0.70)	$ (0.15)
Diluted loss (in dollars per share)	$ (0.70)	$ (0.15)

Loss per Share - Antidilutive S

Loss per Share - Antidilutive Securities (Details) - shares	Jun. 16, 2021	Mar. 31, 2022	Mar. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		27,544,000	0
Earnout Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Contingent consideration liability (in shares)	15,000,000
Vesting Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Contingent consideration liability (in shares)	8,600,000
2016 Plan \| Common Class A
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted shares (in shares)	2,000,000
Series I Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		5,226,000	0
IPO Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		9,867,000	0
Restricted shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		366,000	0
Restricted shares \| Wilco Holdco, Inc.
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		1,248,000	0
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		5,951,000	0
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities (in shares)		4,886,000	0