Balance Sheet Offsetting (Detail) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Financial Assets, Net Amounts Presented In The Consolidated Balance Sheet	$ 24,586,000	$ 24,316,000
Derivative Financial Liabilities, Net Amounts Presented In The Consolidated Balance Sheet	43,164,000	50,247,000
Offsetting Of Financial Assets [Member]
Derivative [Line Items]
Derivative Financial Assets, Gross Amounts Recognized	24,586,000	24,316,000
Derivative Financial Assets, Gross Amounts Offset	0	0
Derivative Financial Assets, Net Amounts Presented In The Consolidated Balance Sheet	24,586,000	24,316,000
Derivative Financial Assets, Financial Instruments	0	0
Derivative Financial Assets, Cash Collateral	(1,250,000)	(3,940,000)
Derivative Financial Assets, Net Amount	23,336,000	20,376,000
Offsetting Of Financial Liabilities [Member]
Derivative [Line Items]
Derivative Financial Liabilities, Gross Amounts Recognized	43,164,000	50,247,000
Derivative Financial Liabilities, Gross Amounts Offset	0	0
Derivative Financial Liabilities, Net Amounts Presented In The Consolidated Balance Sheet	43,164,000	50,247,000
Derivative Financial Liabilities, Financial Instruments	0	0
Derivative Financial Liabilities, Cash Collateral	(43,826,000)	(42,813,000)
Derivative Financial Liabilities, Net Amount	(662,000)	7,434,000
Repurchase Agreements, Gross Amounts Recognized	275,830,000	295,800,000
Repurchase Agreements, Gross Amounts Offset	0	0
Repurchase Agreements, Net Amounts Presented In The Consolidated Balance Sheet	275,830,000	295,800,000
Repurchase Agreements, Financial Instruments	(275,830,000)	(295,800,000)
Repurchase Agreements, Cash Collateral	0	0
Repurchase Agreements, Net Amount	0	0
Financial Liabilities, Gross Amounts Recognized	318,994,000	346,047,000
Financial Liabilities, Gross Amounts Offset	0	0
Financial Liabilities, Net Amounts Presented In The Consolidated Balance Sheet	318,994,000	346,047,000
Financial Liabilities, Financial Instruments	(275,830,000)	(295,800,000)
Financial Liabilities, Cash Collateral	(43,826,000)	(42,813,000)
Financial Liabilities, Net Amount	$ (662,000)	$ 7,434,000