| Document and Entity Information | Jun. 28, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jun. 28, 2023 |
| Entity File Number | 001-39439 |
| Entity Registrant Name | ATI PHYSICAL THERAPY, INC. |
| Entity Central Index Key | 0001815849 |
| 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 |
| Title of 12(b) Security | Class A Common Stock, $0.0001 par value |
| Trading Symbol | ATIP |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
