Stockholders' Equity - Net Income (Loss) Attributable to Noncontrolling Interests (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests	$ 1,423	$ 1,492	$ (4,650)	$ 8,662
Noncontrolling interests	84,885		84,885		$ 71,583
Profits Interest Participation Rights [Member]
Change In Ownership Interest [Line Items]
Noncontrolling interests	2,593		2,593		3,177
Consolidated VIEs [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests	1,253	189	(474)	423
Noncontrolling interests	38,158		38,158		18,241
Edgewater [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests	168	1,302	(4,179)	8,237
Noncontrolling interests	44,119		44,119		50,151
Other Entity [Member]
Change In Ownership Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interests	2	$ 1	3	$ 2
Noncontrolling interests	$ 15		$ 15		$ 14