Derivatives - Offsetting of Derivative Instruments (Detail) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Gross Amounts, derivative assets		$ 27,658	$ 4,448
Gross Amounts Offset, derivative assets		(27,127)	(2,580)
Net Amounts Presented in the Statements of Financial Condition, derivative assets	[1]	531	1,868
Gross Amounts, derivative liabilities		28,970	6,733
Gross Amounts Offset, derivative liabilities		(27,127)	(2,580)
Net Amounts Presented in the Statements of Financial Condition, derivative liabilities	[1]	1,843	4,153
FX/Commodities Options [Member]
Offsetting Assets [Line Items]
Gross Amounts, derivative assets		273	26
Gross Amounts Offset, derivative assets		(2)
Net Amounts Presented in the Statements of Financial Condition, derivative assets	[1]	271	26
Gross Amounts, derivative liabilities		2
Gross Amounts Offset, derivative liabilities		(2)
FX Swaps [Member]
Offsetting Assets [Line Items]
Gross Amounts, derivative assets		222	1,672
Gross Amounts Offset, derivative assets		(24)	(394)
Net Amounts Presented in the Statements of Financial Condition, derivative assets	[1]	198	1,278
Gross Amounts, derivative liabilities		333	2,638
Gross Amounts Offset, derivative liabilities		(24)	(394)
Net Amounts Presented in the Statements of Financial Condition, derivative liabilities	[1]	309	2,244
Forwards [Member]
Offsetting Assets [Line Items]
Gross Amounts, derivative assets		71	706
Gross Amounts Offset, derivative assets		(9)	(142)
Net Amounts Presented in the Statements of Financial Condition, derivative assets	[1]	62	564
Gross Amounts, derivative liabilities		901	1,427
Gross Amounts Offset, derivative liabilities		(9)	(142)
Net Amounts Presented in the Statements of Financial Condition, derivative liabilities	[1]	892	1,285
Futures [Member]
Offsetting Assets [Line Items]
Gross Amounts, derivative assets		27,092	2,044
Gross Amounts Offset, derivative assets		(27,092)	(2,044)
Gross Amounts, derivative liabilities		27,734	2,668
Gross Amounts Offset, derivative liabilities		(27,092)	(2,044)
Net Amounts Presented in the Statements of Financial Condition, derivative liabilities	[1]	$ 642	$ 624

[1] There were no additional balances in gross amounts not offset as of September 30, 2020 and December 31, 2019.