Investments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule Of Investments [Line Items]
Equity method investments	$ 39,600,000		$ 37,700,000
Gains (losses) on equity method investments	1,466,000	$ 1,023,000
Impairment charge on equity method investments	0	2,500,000
Investments	40,004,000		38,008,000
Consolidated VIE, total assets	5,570,665,000		3,949,300,000
Consolidated VIE, total liabilities	4,680,254,000		3,120,397,000
Maximum exposure to loss	4,500,000		4,800,000
Variable Interest Entity, Primary Beneficiary [Member]
Schedule Of Investments [Line Items]
Consolidated VIE, total assets	7,600,000		7,200,000
Consolidated VIE, total liabilities	1,400,000		1,000,000.0
Equity Investments [Member]
Schedule Of Investments [Line Items]
Investments	400,000		$ 400,000
Gains (losses) on equity method investments	0	0
Impairment charges, alternative measurements	0	0
Unrealized gains (losses) to reflect observable transactions	$ 0	$ 40,000