Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under U.S. GAAP Guidance (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Net amounts of recognized assets
Marketable securities	$ 360	$ 349
Government debt	47,959	57,918
Securities owned—Equities	110	75
FX/commodities options		74
Forwards1	690	295
FX swaps	4,553	562
Futures	0	0
Corporate bonds	1,153	579
Total	54,825	59,852
Net amounts of recognized Liabilities
FX swaps	4,551	319
Forwards1	653	215
Futures	1,217	926
Contingent consideration	32,975	39,791
Total	39,396	41,251
Disposal Group, Held-for-sale, Not Discontinued Operations
Net amounts of recognized assets
Forwards1	30
Net amounts of recognized Liabilities
Forwards1	7
Netting and Collateral
Net amounts of recognized assets
Marketable securities	0	0
Government debt	0	0
Securities owned—Equities	0	0
FX/commodities options		0
Forwards1	(258)	(43)
FX swaps	(1,176)	(21)
Futures	(75,703)	(41,257)
Corporate bonds	0	0
Total	(77,137)	(41,321)
Net amounts of recognized Liabilities
FX swaps	(1,176)	(21)
Forwards1	(258)	(43)
Futures	(75,703)	(41,257)
Contingent consideration	0	0
Total	(77,137)	(41,321)
Level 1
Net amounts of recognized assets
Marketable securities	360	349
Government debt	47,959	57,918
Securities owned—Equities	110	75
FX/commodities options		74
Forwards1	0	0
FX swaps	0	0
Futures	0	0
Corporate bonds	0	0
Total	48,429	58,416
Net amounts of recognized Liabilities
FX swaps	0	0
Forwards1	0	0
Futures	0	0
Contingent consideration	0	0
Total	0	0
Level 2
Net amounts of recognized assets
Marketable securities	0	0
Government debt	0	0
Securities owned—Equities	0	0
FX/commodities options		0
Forwards1	948	338
FX swaps	5,729	583
Futures	75,703	41,257
Corporate bonds	1,153	579
Total	83,533	42,757
Net amounts of recognized Liabilities
FX swaps	5,727	340
Forwards1	911	258
Futures	76,920	42,183
Contingent consideration	0	0
Total	83,558	42,781
Level 3
Net amounts of recognized assets
Marketable securities	0	0
Government debt	0	0
Securities owned—Equities	0	0
FX/commodities options		0
Forwards1	0	0
FX swaps	0	0
Futures	0	0
Corporate bonds	0	0
Total	0	0
Net amounts of recognized Liabilities
FX swaps	0	0
Forwards1	0	0
Futures	0	0
Contingent consideration	32,975	39,791
Total	$ 32,975	$ 39,791

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