Intangible Assets - Carrying Value and Amortization of Identifiable Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Total identifiable intangible assets, Gross Carrying Amount	$ 478,130		$ 373,019
Accumulated Amortization	(53,483)		(46,500)
Total identifiable intangible assets, Net (Excluding Goodwill), Total	424,647		326,519
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	5,000		0
Accumulated Amortization	(417)		0
Net Carrying Amount	4,583		0
Customer relationships
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	243,969		143,953
Accumulated Amortization	(43,886)		(38,281)
Net Carrying Amount	200,083		105,672
Favorable leasehold interests
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	13,279		13,295
Accumulated Amortization	(4,742)		(4,319)
Net Carrying Amount	8,537		8,976
Non-compete agreements
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	28,130		28,023
Accumulated Amortization	(4,438)		(3,900)
Net Carrying Amount	23,692		24,123
Customer relationships, non-compete agreements, and U.S. Health Works trademarks
Amortized intangible assets:
Amortization expense	6,400	$ 4,400
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Carrying amount	$ 166,698		166,698
Amortized intangible assets:
Weighted average time until next renewal	8 years 6 months 145 days
Certificates of need
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Carrying amount	$ 19,159		19,155
Accreditations
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Carrying amount	$ 1,895		$ 1,895
Amortized intangible assets:
Weighted average time until next renewal	1 year 6 months