Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 9,101	$ 7,842
Other comprehensive income (loss) before reclassifications	(8,293)	2,359
Amounts reclassified from other comprehensive income	(243)
Period change	(8,536)	2,359
Ending Balance	565	10,201
Unrealized Gains (Losses) on Securities Available-for-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	12,671	11,036
Other comprehensive income (loss) before reclassifications	(9,631)	2,947
Amounts reclassified from other comprehensive income	(243)
Period change	(9,874)	2,947
Ending Balance	2,797	13,983
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3,570)	(3,194)
Other comprehensive income (loss) before reclassifications	1,338	(588)
Period change	1,338	(588)
Ending Balance	$ (2,232)	$ (3,782)