| Document and Entity Information | Jun. 16, 2021 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | true |
| Entity Central Index Key | 0001815849 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K/A |
| Document Period End Date | Jun. 16, 2021 |
| Entity Registrant Name | ATI PHYSICAL THERAPY, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39439 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Amendment Description | On June 23, 2021, ATI Physical Therapy, Inc. (formerly known as Fortress Value Acquisition Corp. II) (the “Company”), filed a Current Report on Form 8-K (the “Original Report”) to report the Closing and related matters under Items 1.01, 2.01, 2.03, 3.02, 4.01, 5.01, 5.01, 5.05 and 9.01 of Form 8-K. Due to the large number of events to be reported under the specified items of Form 8-K, this Amendment No. 1 to Form 8-K is being filed to amend the Original Report to include additional matters related to the transactions under Items 3.03, 5.03 and 5.06 of Form 8-K. This Amendment No. 1 does not amend any other item of the Original Report or purport to provide an update or a discussion of any developments at the Company or its subsidiaries subsequent to the filing date of the Original Report. The information previously reported in or filed with the Original Report is hereby incorporated by reference in this Form 8-K/A. Capitalized terms used herein but not defined herein have the meanings ascribed to such terms in the Original Report. |
| Common Class A [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class A Common Stock, $0.0001 par value |
| Trading Symbol | ATIP |
| Security Exchange Name | NYSE |
| Redeemable Warrants [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 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 |
