Segment Information - Selected Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment information
Net operating revenues	$ 1,267,401	$ 1,077,014	$ 3,816,575	$ 3,270,996
Adjusted EBITDA	156,628	115,827	498,088	413,397
Total assets	5,980,181	5,123,807	5,980,181	5,123,807	$ 5,127,166
Purchases of property and equipment, net	39,391	68,498	121,039	173,800
Operating Segments | Critical Illness Recovery Hospital
Segment information
Net operating revenues	420,108	416,934	1,327,236	1,301,251
Adjusted EBITDA	53,292	46,873	186,989	194,253
Total assets	1,785,336	2,008,485	1,785,336	2,008,485
Purchases of property and equipment, net	8,134	8,003	31,455	28,717
Operating Segments | Rehabilitation Hospital
Segment information
Net operating revenues	176,885	157,499	525,428	453,702
Adjusted EBITDA	25,343	22,581	80,314	62,038
Total assets	888,342	740,276	888,342	740,276
Purchases of property and equipment, net	8,769	29,373	29,766	77,707
Operating Segments | Outpatient Rehabilitation
Segment information
Net operating revenues	265,927	246,644	790,491	751,999
Adjusted EBITDA	34,531	29,298	107,003	102,575
Total assets	991,105	945,765	991,105	945,765
Purchases of property and equipment, net	7,209	6,496	22,565	19,370
Operating Segments | Concentra
Segment information
Net operating revenues	404,481	255,881	1,173,420	763,357
Adjusted EBITDA	68,754	40,003	199,119	125,656
Total assets	2,201,869	1,332,012	2,201,869	1,332,012
Purchases of property and equipment, net	12,539	5,369	29,281	21,656
Other
Segment information
Net operating revenues	0	56	0	687
Adjusted EBITDA	(25,292)	(22,928)	(75,337)	(71,125)
Total assets	113,529	97,269	113,529	97,269
Purchases of property and equipment, net	$ 2,740	$ 19,257	$ 7,972	$ 26,350