Segment Information - Selected Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenue	$ 1,534,221	$ 1,423,869	$ 4,644,704	$ 4,071,219
Adjusted EBITDA	208,577	213,204	808,939	579,289
Total assets	7,899,473	7,659,877	7,899,473	7,659,877	$ 7,655,399
Purchases of property and equipment	48,944	34,319	125,386	105,572
Operating Segments | Critical Illness Recovery Hospital
Segment Reporting Information [Line Items]
Revenue	530,646	519,454	1,669,577	1,539,601
Adjusted EBITDA	57,245	88,830	243,421	267,143
Total assets	2,181,405	2,160,157	2,181,405	2,160,157
Purchases of property and equipment	12,365	11,126	43,249	35,061
Operating Segments | Rehabilitation Hospital
Segment Reporting Information [Line Items]
Revenue	212,434	188,075	632,904	538,761
Adjusted EBITDA	44,076	44,637	145,378	110,811
Total assets	1,191,093	1,144,436	1,191,093	1,144,436
Purchases of property and equipment	4,366	1,636	8,288	6,884
Operating Segments | Outpatient Rehabilitation
Segment Reporting Information [Line Items]
Revenue	274,540	240,042	806,910	662,429
Adjusted EBITDA	38,762	30,623	110,724	51,463
Total assets	1,339,452	1,298,938	1,339,452	1,298,938
Purchases of property and equipment	9,481	7,268	24,264	22,245
Operating Segments | Concentra
Segment Reporting Information [Line Items]
Revenue	442,190	391,859	1,321,402	1,102,732
Adjusted EBITDA	99,832	80,547	318,907	183,510
Total assets	2,609,361	2,355,644	2,609,361	2,355,644
Purchases of property and equipment	11,353	11,985	31,624	34,391
Other
Segment Reporting Information [Line Items]
Revenue	74,411	84,439	213,911	227,696
Adjusted EBITDA	(31,338)	(31,433)	(9,491)	(33,638)
Total assets	578,162	700,702	578,162	700,702
Purchases of property and equipment	$ 11,379	$ 2,304	$ 17,961	$ 6,991