Change in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 580,471	$ 489,051	$ 383,050
Ending Balance	687,336	580,471	489,051
Net Change in Investment Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,887)	446	(20,822)
Other comprehensive income (loss) before reclassifications	(4,838)	(1,417)	21,911
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(1,469)	(916)	(643)
Total other comprehensive (loss) income	(6,307)	(2,333)	21,268
Ending Balance	(8,194)	(1,887)	446
Net Change in Securities Held-To-Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,795	2,207
Other comprehensive income (loss) before reclassifications			2,207
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(403)	(412)
Total other comprehensive (loss) income	(403)	(412)	2,207
Ending Balance	1,392	1,795	2,207
Net Change in Defined Benefit Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	788	847	(472)
Less: Amounts reclassified from accumulated other comprehensive income (loss)	169	(59)	1,319
Total other comprehensive (loss) income	169	(59)	1,319
Ending Balance	957	788	847
Net Change in Fair Value of Derivative Used for Cash Flow Hedge [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(1,772)
Total other comprehensive (loss) income	(1,772)
Ending Balance	(1,772)
Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	696	3,500	(21,294)
Other comprehensive income (loss) before reclassifications	(6,610)	(1,417)	24,118
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(1,703)	(1,387)	676
Total other comprehensive (loss) income	(8,313)	(2,804)	24,794
Ending Balance	$ (7,617)	$ 696	$ 3,500