Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under FASB Guidance (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Net amounts of recognized assets
Government debt	$ 32,027	$ 32,003
Marketable securities	45,002	0
Interest rate swaps	445	782
Foreign exchange swaps, Assets	501
Equity options, Assets	688
Securities owned - Equities	1,092
Total	79,755	32,785
Net amounts of recognized Liabilities
Foreign exchange swaps, Liabilities	926	338
Equity options, Liabilities	925
Securities sold, not yet purchased-Equities, Liabilities	2,031
Total	3,882	338
Level 1 [Member]
Net amounts of recognized assets
Government debt	32,027	32,003
Marketable securities	45,002
Interest rate swaps
Foreign exchange swaps, Assets
Equity options, Assets	688
Securities owned - Equities	1,092
Total	78,809	32,003
Net amounts of recognized Liabilities
Foreign exchange swaps, Liabilities
Equity options, Liabilities	925
Securities sold, not yet purchased-Equities, Liabilities	2,031
Total	2,956
Level 2 [Member]
Net amounts of recognized assets
Government debt
Marketable securities
Interest rate swaps	445	782
Foreign exchange swaps, Assets	501
Equity options, Assets
Securities owned - Equities
Total	946	782
Net amounts of recognized Liabilities
Foreign exchange swaps, Liabilities	926	338
Equity options, Liabilities
Securities sold, not yet purchased-Equities, Liabilities
Total	926	338
Level 3 [Member]
Net amounts of recognized assets
Government debt
Marketable securities
Interest rate swaps
Foreign exchange swaps, Assets
Equity options, Assets
Securities owned - Equities
Total
Net amounts of recognized Liabilities
Foreign exchange swaps, Liabilities
Equity options, Liabilities
Securities sold, not yet purchased-Equities, Liabilities
Total
Netting and Collateral [Member]
Net amounts of recognized assets
Government debt
Marketable securities
Interest rate swaps
Foreign exchange swaps, Assets
Equity options, Assets
Securities owned - Equities
Total
Net amounts of recognized Liabilities
Foreign exchange swaps, Liabilities
Equity options, Liabilities
Securities sold, not yet purchased-Equities, Liabilities
Total