Acquisitions - Proforma Results and Other Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Mar. 04, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Income per common share:
Net cash paid to acquire businesses		$ 27,390	$ 472,206	$ 1,061,628
Issuance of non-controlling interests		18,280	50,178	14,569
Goodwill		2,782,812	2,751,000	2,314,624
Specialty Hospitals
Income per common share:
Goodwill		0	1,447,406	1,357,379
Inpatient rehabilitation
Income per common share:
Goodwill		415,528	0	0
Concentra
Income per common share:
Goodwill		674,542	660,037	650,650
Outpatient Rehabilitation
Income per common share:
Goodwill		647,522	643,557	306,595
Physiotherapy
Income per common share:
Acquisition costs included (excluded) from proforma results			3,200
Net cash paid to acquire businesses	$ 406,304
Goodwill	$ 343,187
Other Acquisitions
Income per common share:
Net cash paid to acquire businesses			65,600	14,400
Issuance of non-controlling interests			38,300	14,700
Transfer of business net assets			17,700
Non-operating gain to bargain purchase			9,500
Consideration transferred		36,100
Consideration transferred, cash		27,400
Other Acquisitions | Specialty Hospitals
Income per common share:
Goodwill			96,800	21,900	$ 800
Other Acquisitions | Inpatient rehabilitation
Income per common share:
Goodwill		12,900
Other Acquisitions | Concentra
Income per common share:
Goodwill		14,500	4,600	4,200
Other Acquisitions | Outpatient Rehabilitation
Income per common share:
Goodwill		$ 3,800	2,300
Pro Forma
Pro forma results of operations
Net revenue			4,339,551	4,477,088
Net income			$ 113,590	$ 119,763
Income per common share:
Basic (in dollars per share)			$ 0.86	$ 0.91
Diluted (in dollars per share)			$ 0.86	$ 0.91
Pro Forma | Physiotherapy
Income per common share:
Acquisition costs included (excluded) from proforma results			$ (3,200)	$ 3,200
Pro Forma | Concentra Inc
Income per common share:
Acquisition costs included (excluded) from proforma results				$ (4,700)