Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under GAAP Guidance (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Net amounts of recognized assets
Marketable securities, Assets	$ 13,220	$ 32,064
Government debt, Assets	58,405	57,788
Securities owned - Equities, Assets	658	620
Foreign exchange/commodities options, Assets	2	39
Forwards, Assets	338	236
Foreign exchange swaps, Assets	3,348	1,611
Futures, Assets	127	93
Corporate bonds, Assets	1,335
Total, Assets	77,433	92,451
Net amounts of recognized Liabilities
Foreign exchange/commodities options, Liabilities	71	88,016
Foreign exchange swaps, Liabilities	2,282	2,072
Forwards, Liabilities	2,604	639
Futures, Liabilities	404	402
Contingent consideration, Liabilities	41,026	45,984
Total, Liabilities	46,387	137,113
Netting and Collateral [Member]
Net amounts of recognized assets
Foreign exchange/commodities options, Assets	(1,020)	(482,712)
Forwards, Assets	(11)	(17)
Foreign exchange swaps, Assets	(221)	(327)
Futures, Assets	(652)	(57,386)
Total, Assets	(1,904)	(540,442)
Net amounts of recognized Liabilities
Foreign exchange/commodities options, Liabilities	(1,020)	(482,712)
Foreign exchange swaps, Liabilities	(221)	(327)
Forwards, Liabilities	(11)	(17)
Futures, Liabilities	(652)	(57,386)
Total, Liabilities	(1,904)	(540,442)
Level 1 [Member]
Net amounts of recognized assets
Marketable securities, Assets	13,220	32,064
Government debt, Assets	58,405	57,788
Securities owned - Equities, Assets	658	620
Foreign exchange/commodities options, Assets	1,022	482,751
Total, Assets	73,305	573,223
Net amounts of recognized Liabilities
Foreign exchange/commodities options, Liabilities	1,091	570,728
Total, Liabilities	1,091	570,728
Level 2 [Member]
Net amounts of recognized assets
Forwards, Assets	349	253
Foreign exchange swaps, Assets	3,569	1,938
Futures, Assets	779	57,479
Corporate bonds, Assets	1,335
Total, Assets	6,032	59,670
Net amounts of recognized Liabilities
Foreign exchange swaps, Liabilities	2,503	2,399
Forwards, Liabilities	2,615	656
Futures, Liabilities	1,056	57,788
Total, Liabilities	6,174	60,843
Level 3 [Member]
Net amounts of recognized Liabilities
Contingent consideration, Liabilities	41,026	45,984
Total, Liabilities	$ 41,026	$ 45,984