Derivative and Hedging Activities - Offsetting of Derivative Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross Amount	$ 57,551	$ 45,898
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	57,551us-gaap_DerivativeAssets	45,898us-gaap_DerivativeAssets
Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	3,982	2,296
Subject to Master Netting Arrangement [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	3,937	2,109
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	3,937	2,109
Subject to Master Netting Arrangement [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	6	140
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	6	140
Subject to Master Netting Arrangement [Member] \| Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	39	47
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	39	47
Not Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	53,569	43,602
Not Subject to Master Netting Arrangement [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	53,569	43,602
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	$ 53,569	$ 43,602

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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