| In millions, except per share items | Jun-30-23 | Mar-31-23 | Dec-31-22 | Sep-30-22 | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 |
| | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q |
| Net revenue | 172.3 | 166.9 | 161.8 | 156.8 | 163.3 | 153.8 | 155.8 | 159.0 |
| Net revenue growth | 5.5% | 8.5% | 3.9% | -1.4% | -0.5% | 3.2% | 1.7% | -257615.1% |
| Cost of services: | | | | | | | | |
| Salaries and related costs | 95.3 | 90.7 | 90.7 | 90.3 | 89.6 | 87.4 | 88.1 | 86.8 |
| Rent, clinic supplies, contract labor and other | 50.4 | 52.9 | 49.1 | 51.4 | 50.4 | 51.6 | 47.8 | 45.8 |
| Provision for doubtful accounts | 2.4 | 4.1 | 2.5 | 2.8 | 3.5 | 5.1 | 2.1 | 3.5 |
| Total cost of services | 148.1 | 147.7 | 356.6 | 366.8 | 392.8 | 417.3 | 256.0 | 762.7 |
| Selling, general and administrative expenses | 36.6 | 30.6 | 27.6 | 25.3 | 31.8 | 30.0 | 29.9 | 30.8 |
| Goodwill, intangible and other asset impairment charges | | | 96.0 | 106.7 | 127.8 | 155.7 | | 509.0 |
| Operating loss | -12.4 | -11.4 | -104.1 | -119.7 | -139.9 | -176.1 | -12.1 | -516.9 |
| Operating margin | -7.2% | -6.8% | -64.4% | -76.3% | -85.6% | -114.5% | -7.8% | -325.0% |
| Change in fair value of 2L Notes | -7.0 | | | | | | | |
| Change in fair value of warrant liability | -0.2 | 0.2 | -0.6 | -0.8 | -1.2 | -1.7 | -2.2 | -15.9 |
| Change in fair value of contingent common shares liability | -0.8 | -0.7 | -9.8 | -6.9 | -1.5 | -24.3 | -7.9 | -146.3 |
| Interest expense, net | 16.7 | 13.9 | 13.5 | 11.8 | 11.4 | 8.7 | 7.2 | 7.4 |
| Other expense, net | 0.6 | 0.4 | 6.5 | -0.2 | 0.2 | 2.8 | 6.1 | -0.1 |
| Loss before taxes | -21.7 | -25.1 | -107.4 | -123.9 | -148.8 | -161.5 | -3.7 | -362.1 |
| Income tax expense (benefit) | 0.1 | 0.1 | -5.0 | -7.2 | -13.0 | -23.3 | -5.4 | -35.3 |
| Net loss | -21.7 | -25.1 | -107.4 | -123.9 | -148.8 | -161.5 | -3.7 | -362.1 |
| Net income (loss) attributable to non-controlling interests | 1.0 | 1.1 | 0.4 | -0.4 | -0.2 | -0.5 | 0.9 | -2.1 |
| Net loss attributable to ATI Physical Therapy, Inc. | -22.7 | -26.3 | -102.8 | -116.3 | -135.5 | -137.8 | 0.8 | -324.7 |
| Less: Series A Senior Preferred Stock redemption value adjustments | 44.7 | | | | | | | |
| Less: Series A Senior Preferred Stock cumulative dividend | 5.7 | | | | 5.1 | | | |
| Loss available to common stockholders, diluted | 0.0 | | | | 0.0 | | | |
| Loss available to common stockholders, basic | -73.1 | -26.2 | -107.8 | -123.5 | -140.6 | -161.0 | -4.6 | -360.0 |
| |
| Loss per share of Class A common stock: | | | | | | | | |
| Basic (in dollars per share) | ($17.74) | ($0.15) | ($0.53) | ($0.60) | ($34.49) | ($0.70) | $0.33 | ($1.65) |
| Diluted (in dollars per share) | ($17.74) | ($0.15) | ($0.53) | ($0.60) | ($34.49) | ($0.70) | $0.33 | ($1.65) |
| |
| Weighted average shares outstanding: | | | | | | | | |
| Basic (in shares) | 4.1 | 204.9 | 203.2 | 204.3 | 4.1 | 200.0 | 165.8 | 197.0 |
| Diluted (in shares) | 4.1 | 204.9 | 203.2 | 204.3 | 4.1 | 200.0 | 165.8 | 197.0 |