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Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Investments [Line Items]
Equity method investments	$ 40,000,000	$ 35,211,000
Gains (losses) on equity method investments	4,115,000	7,377,000	$ 4,627,000
Gains (losses) relating to cost method investments			$ 0
Investments	40,349,000	35,403,000
Consolidated VIE, total assets	3,916,120,000	3,432,757,000
Consolidated VIE, total liabilities	3,148,745,000	2,544,877,000
Maximum exposure to loss	2,800,000	2,100,000
Variable Interest Entity, Primary Beneficiary [Member]
Schedule Of Investments [Line Items]
Consolidated VIE, total assets	7,400,000	4,900,000
Consolidated VIE, total liabilities	2,100,000	600,000
Equity Investments [Member]
Schedule Of Investments [Line Items]
Investments	400,000	200,000
Unrealized gains to reflect observable transactions	22,800,000	38,000,000.0
Gains (losses) on equity method investments	0	0
Impairment charges, alternative measurements	$ 0	$ 0

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