Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net (loss) income attributable to ATI Physical Therapy, Inc.	$ (331,711)		$ 121		$ (786,195)	$ (6,574)
Other comprehensive income (loss):
Unrealized gain (loss) on interest rate swap	181	[1]	(1,133)	[2]	1,378	(692)
Comprehensive loss	$ (331,530)		$ (1,012)		$ (784,817)	$ (7,266)

[1] Other comprehensive income related to unrealized gain on interest rate swap(2)Refer to Note 2 - Basis of Presentation and Recent Accounting Standards

[2] Other comprehensive income (loss) related to unrealized gain (loss) on interest rate swap