Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	As reported	Retrospective application of reverse recapitalization	Common Stock	Common Stock As reported	Common Stock Retrospective application of reverse recapitalization	Treasury Stock	Treasury Stock As reported	Treasury Stock Retrospective application of reverse recapitalization	Additional Paid-In Capital	Additional Paid-In Capital As reported	Additional Paid-In Capital Retrospective application of reverse recapitalization	Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income As reported	Accumulated Other Comprehensive (Loss) Income Retrospective application of reverse recapitalization	Accumulated Deficit	Accumulated Deficit As reported	Accumulated Deficit Retrospective application of reverse recapitalization	Non-Controlling Interests	Non-Controlling Interests As reported	Non-Controlling Interests Retrospective 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)	10,000.00			(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