Redeemable Non-Controlling Interests - Schedule of Redeemable Non-Controlling Interests (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, beginning	$ 521,552	$ 445,931	$ 398,171	$ 495,987	$ 620,377	$ 974,541
Net income attributable to redeemable non-controlling interests	12,580	18,073	9,626	17,328	3,264	7,256
Distributions to and purchases of redeemable non-controlling interests	(2,967)	(1,987)	(614)	(4,171)	(30)	(5,687)
Purchase of membership interests of Concentra Group Holdings Parent			0			(366,203)
Redemption value adjustment on redeemable non-controlling interests	96,000	59,370	38,405	32,555	(127,916)	10,123
Other	165	165	343	157	292	347
Balance, ending	$ 627,330	$ 521,552	$ 445,931	$ 541,856	$ 495,987	$ 620,377