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Investments - Additional Information (Detail) - USD ($)
 3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Schedule Of Investments [Line Items]      
Equity method investments $ 38,600,000   $ 40,000,000.0
Gains (losses) on equity method investments 1,023,000 $ 783,000  
Impairment charge on equity method investments 2,500,000 0  
Investments 38,966,000   40,349,000
Consolidated VIE, total assets 5,728,159,000   3,916,120,000
Consolidated VIE, total liabilities 4,988,746,000   3,148,745,000
Maximum exposure to loss 2,100,000   2,800,000
Variable Interest Entity, Primary Beneficiary [Member]      
Schedule Of Investments [Line Items]      
Consolidated VIE, total assets 6,600,000   7,400,000
Consolidated VIE, total liabilities 2,500,000   2,100,000
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 $ (40,300) $ 20,400,000