Intangible Assets - Carrying Amount of Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)
Goodwill
Goodwill, Beginning Balance	$ 3,379,014
Acquisition of businesses	20,780
Goodwill, Ending Balance	3,399,794
Critical Illness Recovery Hospital
Goodwill
Goodwill, Beginning Balance	1,084,761
Acquisition of businesses	0
Goodwill, Ending Balance	1,084,761
Rehabilitation Hospital
Goodwill
Goodwill, Beginning Balance	432,753
Acquisition of businesses	9,402
Goodwill, Ending Balance	442,155
Outpatient Rehabilitation
Goodwill
Goodwill, Beginning Balance	646,433
Acquisition of businesses	3,621
Goodwill, Ending Balance	650,054
Concentra
Goodwill
Goodwill, Beginning Balance	1,215,067
Acquisition of businesses	7,757
Goodwill, Ending Balance	$ 1,222,824