Change in Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (12,507)	$ 7,097	$ (21,294)	$ 12,943
Other comprehensive income (loss) before reclassifications	9,738	(19,316)	18,884	(24,143)
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(226)	(562)	(585)	(1,581)
Total other comprehensive (loss) income	9,512	(19,878)	18,299	(25,724)
Ending Balance	(2,995)	(12,781)	(2,995)	(12,781)
Net Unrealized (Losses) Gains on Investment Securities Available-for-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12,035)	7,569	(20,822)	13,415
Other comprehensive income (loss) before reclassifications	9,678	(19,316)	18,824	(24,143)
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(226)	(562)	(585)	(1,581)
Total other comprehensive (loss) income	9,452	(19,878)	18,239	(25,724)
Ending Balance	(2,583)	(12,309)	(2,583)	(12,309)
Net Unrealized Losses on Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(472)	(472)	(472)	(472)
Other comprehensive income (loss) before reclassifications	60		60
Less: Amounts reclassified from accumulated other comprehensive income (loss)
Total other comprehensive (loss) income	60		60
Ending Balance	$ (412)	$ (472)	$ (412)	$ (472)