Basis of Presentation and Principles of Consolidation - VIE (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($) item	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Variable interest entity
Number of professional associations consolidated as VIEs | item					2
Number of professional corporations consolidated as VIEs | item					11
Number of service corporations consolidated as VIEs | item					1
Revenue	$ 241,030		$ 130,276		$ 421,829	$ 258,849
Net (loss) income	(25,682)	$ (29,603)	(29,324)	$ (30,150)	(55,285)	(59,474)
Assets	2,418,828				2,418,828		$ 1,602,827
Deficit	(1,294,929)	$ (1,000,177)	(1,002,640)	$ (1,001,558)	(1,294,929)	(1,002,640)	(1,014,025)	$ (1,013,119)
Primary beneficiary
Variable interest entity
Revenue	57,700		17,400		100,200	38,500
Net (loss) income	900		$ (200)		800	$ (300)
Assets	22,900				22,900		13,600
Liabilities	59,800				59,800		51,300
Deficit	$ 36,900				$ 36,900		$ 37,700