Offsetting Derivatives Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 25,776	$ 38,125
Gross Amounts of Recognized Financial Liabilities Set Off in the Balance Sheet	8,380	15,827
Derivative cash Collateral Held, Obligation to Return Cash	16,273	11,405
Net Amounts of Assets Presented in the Balance Sheet	1,123	10,893
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	1,123	8,158
Gross Amounts Not Offset in the Balance Sheet, Cash Collateral Received (excluding) Surplus Collateral)	0	0
Net Amount	0	2,735
Fair Value of Financial Instruments Received as Collateral Not Set Off in the Balance Sheet	8,177	9,260
Derivatives
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	25,776	38,125
Gross Amounts of Recognized Financial Liabilities Set Off in the Balance Sheet	8,380	15,827
Derivative cash Collateral Held, Obligation to Return Cash	16,273	11,405
Net Amounts of Assets Presented in the Balance Sheet	1,123	10,893
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	1,123	8,158
Gross Amounts Not Offset in the Balance Sheet, Cash Collateral Received (excluding) Surplus Collateral)	0	0
Net Amount	0	2,735
Fair Value of Financial Instruments Received as Collateral Not Set Off in the Balance Sheet	$ 8,177	$ 9,260