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Related Party Transactions - Additional Information (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
Related Party Transaction [Line Items]          
Securities owned, at fair value $ 32,574   $ 32,574   $ 17,319
Gains and losses related to certain WisdomTree ETFs 86 $ 64 94 $ 212  
WisdomTree ETF [Member]          
Related Party Transaction [Line Items]          
Securities owned, at fair value $ 23,906   $ 23,906   $ 16,886