Intangible Assets - Carrying Value and Amortization of Identifiable Intangible Assets and Liabilities (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
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Total identifiable intangible assets, gross carrying amount	$ 515,146		$ 515,146		$ 373,019
Finite-lived intangible assets, accumulated amortization	(70,299)		(70,299)		(46,500)
Total identifiable intangible assets, net carrying amount	444,847		444,847		326,519
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	5,000		5,000		0
Finite-lived intangible assets, accumulated amortization	(3,333)		(3,333)		0
Finite-lived intangible assets, net carrying amount	1,667		1,667		0
Customer relationships
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	279,967		279,967		143,953
Finite-lived intangible assets, accumulated amortization	(55,760)		(55,760)		(38,281)
Finite-lived intangible assets, net carrying amount	224,207		224,207		105,672
Favorable leasehold interests
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	13,553		13,553		13,295
Finite-lived intangible assets, accumulated amortization	(5,653)		(5,653)		(4,319)
Finite-lived intangible assets, net carrying amount	7,900		7,900		8,976
Non-compete agreements
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	28,953		28,953		28,023
Finite-lived intangible assets, accumulated amortization	(5,553)		(5,553)		(3,900)
Finite-lived intangible assets, net carrying amount	23,400		23,400		24,123
Customer relationships, non-compete agreements, and trademarks
Amortized intangible assets:
Amortization expense	7,900	$ 4,400	22,100	$ 13,100
Estimated amortization expense
2018	7,811		7,811
2019	26,490		26,490
2020	25,864		25,864
2021	25,648		25,648
2022	25,443		25,443
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible assets, carrying amount	166,698		$ 166,698		166,698
Amortized intangible assets:
Weighted average time until next renewal			8 years 4 months 24 days
Certificates of need
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible assets, carrying amount	19,118		$ 19,118		19,155
Accreditations
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible assets, carrying amount	$ 1,857		$ 1,857		$ 1,895
Amortized intangible assets:
Weighted average time until next renewal			1 year 6 months