Restatement of Previously Issued Condensed Consolidated Financial Statements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Comprehensive loss	$ 17,303	$ 59,233	$ 155,663	$ 260,578
Less: Comprehensive loss attributable to noncontrolling interests and redeemable noncontrolling interests	(5,349)	(7,484)	(25,219)	(21,719)
Comprehensive loss attributable to Class A and Class B stockholders	$ 11,954	51,749	$ 130,444	238,859
Restatement Impacts
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Comprehensive loss		5,000		13,900	$ (5,800)	$ 1,800
Less: Comprehensive loss attributable to noncontrolling interests and redeemable noncontrolling interests		$ 9,900		$ 29,600