Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Gains and losses related to certain WisdomTree ETFs	$ 40	$ (406)	$ 26
WisdomTree ETF [Member]
Related Party Transaction [Line Items]
Investment	$ 16,886	$ 7,117

Amount of realized and unrealized gain (loss) on investment.

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