Basis of Presentation and Principles of Consolidation - VIE (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) item	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Variable interest entity
Number of professional associations consolidated as VIEs | item	3
Number of professional corporations consolidated as VIEs | item	13
Number of service corporations consolidated as VIEs | item	1
Revenue	$ 453,675	$ 180,799
Net (loss) income	(199,649)	(29,603)
Assets	17,582,358		$ 17,755,281
(Equity) deficit	(15,829,498)	(1,000,177)	(15,883,804)	$ (1,014,025)
Primary beneficiary
Variable interest entity
Revenue	51,800	42,500
Net (loss) income	(2,100)	$ (100)
Assets	39,200		28,700
Liabilities	78,400		65,800
(Equity) deficit	$ 39,200		$ 37,100