Intangible Assets - Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill
Balance at the beginning of the year	$ 2,751,000	$ 2,314,624
Acquired	31,986	446,702
Measurement period adjustment	(174)	4,825
Sold		(15,151)
Reorganization of reporting units	0
Balance at the end of the year	2,782,812	2,751,000
Long Term Acute Care
Goodwill
Balance at the beginning of the year	0	0
Acquired	0	0
Measurement period adjustment	0	0
Sold		0
Reorganization of reporting units	1,045,220
Balance at the end of the year	1,045,220	0
Inpatient Rehabilitation
Goodwill
Balance at the beginning of the year	0	0
Acquired	12,887	0
Measurement period adjustment	0	0
Sold		0
Reorganization of reporting units	402,641
Balance at the end of the year	415,528	0
Specialty Hospitals
Goodwill
Balance at the beginning of the year	1,447,406	1,357,379
Acquired	797	96,785
Measurement period adjustment	(342)	0
Sold		(6,758)
Reorganization of reporting units	(1,447,861)
Balance at the end of the year	0	1,447,406
Outpatient Rehabilitation
Goodwill
Balance at the beginning of the year	643,557	306,595
Acquired	3,797	345,355
Measurement period adjustment	168	0
Sold		(8,393)
Reorganization of reporting units	0
Balance at the end of the year	647,522	643,557
Concentra
Goodwill
Balance at the beginning of the year	660,037	650,650
Acquired	14,505	4,562
Measurement period adjustment	0	4,825
Sold		0
Reorganization of reporting units	0
Balance at the end of the year	$ 674,542	$ 660,037