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Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Detail) - USD ($) $ in Thousands | Jun. 30, 2016 | Dec. 31, 2015
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Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | $ 3,451 | $ 14,543
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (3,451) | (10,825)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | (2,725)
Net Amount, Derivatives, Financial Assets | 0 | 993
Net Amount Recognized, Resell agreements, Financial Assets | 14,142 | 13,442
Gross Amounts Not Offset Financial Instruments, Resell Agreements | 0 | 0
Gross Amounts Not Offset Collateral, Resell Agreements, Financial Assets | (14,142) | (13,442)
Net Amount, Financial Assets, Resell Agreements | 0 | 0
Net Amount Recognized, Total Financial Assets | 17,593 | 27,985
Gross Amounts Not Offset Collateral, Financial Assets | (14,142) | (16,167)
Net Amount, Financial Assets | 0 | 993
Net Amount Recognized, Derivatives, Financial Liabilities | 68,640 | 40,198
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (3,451) | (10,825)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (62,897) | (28,803)
Net Amount, Derivatives, Financial Liabilities | 2,292 | 570
Net Amount Recognized, Repurchase Agreements, Financial Liabilities | 720,860 | 883,947
Gross Amounts Not Offset Financial Instruments, Repurchase Agreements, Financial Liabilities | 0 | 0
Gross Amounts Not Offset Collateral, Repurchase Agreements, Financial Liabilities | (720,860) | (883,947)
Net Amount, Repurchase Agreements, Financial Liabilities | 0 | 0
Net Amount Recognized, Financial Liabilities | 789,500 | 924,145
Gross Amounts Not Offset Collateral, Financial Liabilities | (783,757) | (912,750)
Net Amount, Financial Liabilities | 2,292 | 570
Counterparty A [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 196 | 743
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (196) | (743)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | 0
Net Amount, Derivatives, Financial Assets | 0 | 0
Net Amount Recognized, Derivatives, Financial Liabilities | 20,942 | 16,092
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (196) | (743)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (20,746) | (15,347)
Net Amount, Derivatives, Financial Liabilities | 0 | 2
Counterparty B [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 2,139 | 6,901
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (2,139) | (5,795)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | (413)
Net Amount, Derivatives, Financial Assets | 0 | 693
Net Amount Recognized, Derivatives, Financial Liabilities | 10,815 | 5,795
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (2,139) | (5,795)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (7,776) | 0
Net Amount, Derivatives, Financial Liabilities | 900 | 0
Counterparty C [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 1,038 | 6,059
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (1,038) | (3,447)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | (2,312)
Net Amount, Derivatives, Financial Assets | 0 | 300
Net Amount Recognized, Derivatives, Financial Liabilities | 4,501 | 3,447
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (1,038) | (3,447)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (3,002) | 0
Net Amount, Derivatives, Financial Liabilities | 461 | 0
Other Counterparties [Member] |  |
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] |  |
Net Amount Recognized, Derivatives, Financial Assets | 78 | 840
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets | (78) | (840)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets | 0 | 0
Net Amount, Derivatives, Financial Assets | 0 | 0
Net Amount Recognized, Derivatives, Financial Liabilities | 32,382 | 14,864
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities | (78) | (840)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities | (31,373) | (13,456)
Net Amount, Derivatives, Financial Liabilities | $ 931 | $ 568

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