Derivatives - Credit Value Adjustment Recorded Related to Notional Amount of Derivatives Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative, Fair Value, Net	$ 78	$ 2,207
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	268,738	223,448
Credit Default Swap, Buying Protection [Member]
Derivative [Line Items]
Derivative, Notional Amount	84,758	71,390
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ (19,274)	$ 0