Intangible Assets - Carrying Value and Amortization of Identifiable Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Total identifiable intangible assets, Gross Carrying Amount	$ 513,760		$ 513,760		$ 373,019
Accumulated Amortization	(61,828)		(61,828)		(46,500)
Total identifiable intangible assets, Net (Excluding Goodwill), Total	451,932		451,932		326,519
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	5,000		5,000		0
Accumulated Amortization	(2,083)		(2,083)		0
Net Carrying Amount	2,917		2,917		0
Customer relationships
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	278,969		278,969		143,953
Accumulated Amortization	(49,617)		(49,617)		(38,281)
Net Carrying Amount	229,352		229,352		105,672
Favorable leasehold interests
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	13,553		13,553		13,295
Accumulated Amortization	(5,148)		(5,148)		(4,319)
Net Carrying Amount	8,405		8,405		8,976
Non-compete agreements
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	28,472		28,472		28,023
Accumulated Amortization	(4,980)		(4,980)		(3,900)
Net Carrying Amount	23,492		23,492		24,123
Customer relationships, non-compete agreements, and trademarks
Amortized intangible assets:
Amortization expense	7,800	$ 4,300	14,200	$ 8,700
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Carrying amount	166,698		$ 166,698		166,698
Amortized intangible assets:
Weighted average time until next renewal			8 years 8 months 12 days
Certificates of need
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Carrying amount	19,173		$ 19,173		19,155
Accreditations
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Carrying amount	$ 1,895		$ 1,895		$ 1,895
Amortized intangible assets:
Weighted average time until next renewal			1 year 6 months