Offsetting of Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition	$ 99,992	$ 159,327
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	94,204	151,419
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received	540	582
Asset Net Amount	5,248	7,326
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	132,187	320,634
Gross Amount of Liabilities Not Offset in the Statement of Financial Condition, Financial Instruments	123,116	319,377
Gross Amounts of Liabilities Not Offset in the Statement of Financial Condition, Cash Collateral Pledged	9,040	1,257
Liability Net Amount	31
Repurchase Agreements
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	122,349	316,352
Gross Amount of Liabilities Not Offset in the Statement of Financial Condition, Financial Instruments	121,880	316,352
Gross Amounts of Liabilities Not Offset in the Statement of Financial Condition, Cash Collateral Pledged	469
Freestanding Derivatives
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition	6,454	10,343
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	1,236	3,025
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received	540	582
Asset Net Amount	4,678	6,736
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	9,838	4,282
Gross Amount of Liabilities Not Offset in the Statement of Financial Condition, Financial Instruments	1,236	3,025
Gross Amounts of Liabilities Not Offset in the Statement of Financial Condition, Cash Collateral Pledged	8,571	1,257
Liability Net Amount	31
Reverse Repurchase Agreements
Offsetting Assets and Liabilities [Line Items]
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition	93,538	148,984
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	92,968	148,394
Asset Net Amount	$ 570	$ 590