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Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Detail) - USD ($) $ in Thousands | Sep. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | $ 16,036 | $ 29,921
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (14,140) | (20,436)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | (1,426) | (6,035)
Net Amount, Derivatives, Financial Assets | 470 | 3,450
Net Amount Recognized, Resell agreements | 13,642 | 9,642
Gross Amounts Not Offset Financial Instruments, Resell Agreements | 0 | 0
Gross Amounts Not Offset Collateral, Resell Agreements, Financial Assets | (13,642) | (9,642)
Net Amount, Financial Assets, Resell Agreements | 0 | 0
Net Amount Recognized, Total Financial Assets | 29,678 | 39,563
Gross Amounts Not Offset Collateral, Financial Assets | (15,068) | (15,677)
Net Amount, Financial Assets | 470 | 3,450
Net Amount Recognized, Derivatives, Financial Liabilities | 52,291 | 47,898
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (14,140) | (20,436)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (37,144) | (26,307)
Net Amount, Derivatives, Financial Liabilities | 1,007 | 1,155
Net Amount Recognized, Repurchase Agreements, Financial Liabilities | 618,504 | 791,119
Gross Amounts Not Offset Financial Instruments, Repurchase Agreements, Financial Liabilities | 0 | 0
Gross Amounts Not Offset Collateral, Repurchase Agreements, Financial Liabilities | (618,504) | (791,119)
Net Amount, Repurchase Agreements, Financial Liabilities | 0 | 0
Net Amount Recognized, Financial Liabilities | 670,795 | 839,017
Gross Amounts Not Offset Collateral, Financial Liabilities | (655,648) | (817,426)
Net Amount, Financial Liabilities | 1,007 | 1,155
Counterparty A [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 593 | 627
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (593) | (627)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | 0
Net Amount, Derivatives, Financial Assets | 0 | 0
Net Amount Recognized, Derivatives, Financial Liabilities | 19,368 | 18,653
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (593) | (627)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (18,611) | (17,626)
Net Amount, Derivatives, Financial Liabilities | 164 | 400
Counterparty B [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 10,048 | 17,308
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (8,383) | (9,506)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | (1,196) | (4,925)
Net Amount, Derivatives, Financial Assets | 469 | 2,877
Net Amount Recognized, Derivatives, Financial Liabilities | 8,383 | 9,506
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (8,383) | (9,506)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | 0 | 0
Net Amount, Derivatives, Financial Liabilities | 0 | 0
Counterparty C [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 3,925 | 7,991
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (3,925) | (7,539)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | 0
Net Amount, Derivatives, Financial Assets | 0 | 452
Net Amount Recognized, Derivatives, Financial Liabilities | 4,522 | 7,539
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (3,925) | (7,539)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (597) | 0
Net Amount, Derivatives, Financial Liabilities | 0 | 0
Other Counterparties [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 1,470 | 3,995
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (1,239) | (2,764)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | (230) | (1,110)
Net Amount, Derivatives, Financial Assets | 1 | 121
Net Amount Recognized, Derivatives, Financial Liabilities | 20,018 | 12,200
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (1,239) | (2,764)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (17,936) | (8,681)
Net Amount, Derivatives, Financial Liabilities | $ 843 | $ 755

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