Intangible Assets - Carrying Value and Amortization of Identifiable Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Total identifiable intangible assets, gross carrying amount	$ 531,499		$ 531,499		$ 517,658
Finite-lived intangible assets, accumulated amortization	(153,066)		(153,066)		(130,117)
Total identifiable intangible assets, net carrying amount	378,433		378,433		387,541
Amortized intangible assets:
Amortization expense	7,400	$ 6,900	21,800	$ 20,600
Trademarks
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	5,000		5,000		5,000
Finite-lived intangible assets, accumulated amortization	(5,000)		(5,000)		(5,000)
Finite-lived intangible assets, net carrying amount	0		0		0
Customer relationships
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	303,424		303,424		291,923
Finite-lived intangible assets, accumulated amortization	(133,859)		(133,859)		(113,346)
Finite-lived intangible assets, net carrying amount	169,565		169,565		178,577
Non-compete agreements
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets, gross carrying amount	35,959		35,959		33,771
Finite-lived intangible assets, accumulated amortization	(14,207)		(14,207)		(11,771)
Finite-lived intangible assets, net carrying amount	21,752		21,752		22,000
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
Certificates of need
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible assets, carrying amount	18,544		$ 18,544		18,392
Accreditations
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible assets, carrying amount	$ 1,874		$ 1,874		$ 1,874
Amortized intangible assets:
Weighted average time until next renewal			1 year 6 months