Segment Information - Reconciliation of Adjusted EBITDA to Income Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment information
Adjusted EBITDA	$ 156,628	$ 115,827	$ 498,088	$ 413,397
Depreciation and amortization	(50,527)	(38,772)	(149,022)	(119,644)
Income (loss) from operations	99,837	72,098	328,996	279,526
Loss on early retirement of debt			(10,255)	(19,719)
Equity in earnings of unconsolidated subsidiaries	5,432	4,431	14,914	15,618
Non-operating gain (loss)	2,139	0	9,016	(49)
Interest expense	(50,669)	(37,688)	(147,991)	(116,196)
Income (loss) before income taxes	56,739	38,841	194,680	159,180
Operating Segments | Critical Illness Recovery Hospital
Segment information
Adjusted EBITDA	53,292	46,873	186,989	194,253
Depreciation and amortization	(11,136)	(10,932)	(34,146)	(34,891)
Stock compensation expense	0	0	0	0
U.S. HealthWorks acquisition costs			0
Income (loss) from operations	42,156	35,941	152,843	159,362
Operating Segments | Rehabilitation Hospital
Segment information
Adjusted EBITDA	25,343	22,581	80,314	62,038
Depreciation and amortization	(6,079)	(4,505)	(17,816)	(14,500)
Stock compensation expense	0	0	0	0
U.S. HealthWorks acquisition costs			0
Income (loss) from operations	19,264	18,076	62,498	47,538
Operating Segments | Outpatient Rehabilitation
Segment information
Adjusted EBITDA	34,531	29,298	107,003	102,575
Depreciation and amortization	(6,597)	(5,964)	(19,938)	(18,182)
Stock compensation expense	0	0	0	0
U.S. HealthWorks acquisition costs			0
Income (loss) from operations	27,934	23,334	87,065	84,393
Operating Segments | Concentra
Segment information
Adjusted EBITDA	68,754	40,003	199,119	125,656
Depreciation and amortization	(24,488)	(15,014)	(70,332)	(46,566)
Stock compensation expense	(767)	(212)	(2,116)	(782)
U.S. HealthWorks acquisition costs			(2,895)
Income (loss) from operations	43,499	24,777	123,776	78,308
Other
Segment information
Adjusted EBITDA	(25,292)	(22,928)	(75,337)	(71,125)
Depreciation and amortization	(2,227)	(2,357)	(6,790)	(5,505)
Stock compensation expense	(5,497)	(4,745)	(15,059)	(13,445)
U.S. HealthWorks acquisition costs			0
Income (loss) from operations	$ (33,016)	$ (30,030)	$ (97,186)	$ (90,075)