Collateralized Transactions - Schedule of Gross Amounts and Offsetting Amounts of Reverse Repurchase Agreements, Repurchase Agreements, Securities Borrowed and Securities Lending Transactions (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Securities Financing Transaction [Line Items]
Net Amounts of Assets Presented on the Balance Sheet	$ 250,000	$ 184,825
Net Amounts of Liabilities Presented on the Balance Sheet	816,606	757,491
Gross Amounts of Recognized Assets	560,002	663,566
Gross Amounts Offset in the Balance Sheet	(64,796)	(204,614)
Net Amounts of Assets Presented on the Balance Sheet	495,206	458,952
Financial Instruments	489,762	449,241
Net Amount	5,444	9,711
Gross Amounts of Recognized Liabilities	1,084,987	1,173,726
Gross Amounts Offset in the Balance Sheet	(64,796)	(204,614)
Net Amounts of Liabilities Presented on the Balance Sheet	1,020,191	969,112
Financial Instruments	1,007,670	957,974
Net Amount	12,521	11,138
Reverse Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Gross Amounts of Recognized Assets	314,796	389,439
Gross Amounts Offset in the Balance Sheet	(64,796)	(204,614)
Net Amounts of Assets Presented on the Balance Sheet	250,000	184,825
Financial Instruments	250,000	183,305
Net Amount	0	1,520
Securities Borrowed [Member]
Securities Financing Transaction [Line Items]
Gross Amounts of Recognized Assets	245,206	274,127
Net Amounts of Assets Presented on the Balance Sheet	245,206	274,127
Financial Instruments	239,762	265,936
Net Amount	5,444	8,191
Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Gross Amounts of Recognized Liabilities	881,402	962,105
Gross Amounts Offset in the Balance Sheet	(64,796)	(204,614)
Net Amounts of Liabilities Presented on the Balance Sheet	816,606	757,491
Financial Instruments	811,335	753,003
Net Amount	5,271	4,488
Securities Loaned [Member]
Securities Financing Transaction [Line Items]
Gross Amounts of Recognized Liabilities	203,585	211,621
Net Amounts of Liabilities Presented on the Balance Sheet	203,585	211,621
Financial Instruments	196,335	204,971
Net Amount	$ 7,250	$ 6,650