Change in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 11,454	$ 7,601	$ 696	$ 3,500
Other comprehensive income (loss) before reclassifications	4,683	(6,024)	15,255	(1,457)
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(460)	(348)	(274)	(814)
Total other comprehensive (loss) income	4,223	(6,372)	14,981	(2,271)
Ending Balance	15,677	1,229	15,677	1,229
Net Change in Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	8,496	4,733	(1,887)	446
Other comprehensive income (loss) before reclassifications	4,683	(6,024)	15,255	(1,457)
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(338)	(296)	(527)	(576)
Total other comprehensive (loss) income	4,345	(6,320)	14,728	(2,033)
Ending Balance	12,841	(1,587)	12,841	(1,587)
Net Change in Securities Held-to-maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,692	2,036	1,795	2,207
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(100)	(37)	(203)	(208)
Total other comprehensive (loss) income	(100)	(37)	(203)	(208)
Ending Balance	1,592	1,999	1,592	1,999
Net Change in Defined Benefit Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,266	832	788	847
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(22)	(15)	456	(30)
Total other comprehensive (loss) income	(22)	(15)	456	(30)
Ending Balance	$ 1,244	$ 817	$ 1,244	$ 817