Change in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 687,336	$ 580,471
Ending Balance	704,001	597,580
Net change in investment securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(8,194)	(1,887)
Other comprehensive income (loss) before reclassifications	1,272	10,572
Less: Amounts reclassified from accumulated other comprehensive loss	(206)	(189)
Net current-period other comprehensive income (loss)	1,066	10,383
Ending Balance	(7,128)	8,496
Net change in securities held to maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	1,392	1,795
Other comprehensive income (loss) before reclassifications	0	0
Less: Amounts reclassified from accumulated other comprehensive loss	(101)	(103)
Net current-period other comprehensive income (loss)	(101)	(103)
Ending Balance	1,291	1,692
Net change in defined benefit plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	957	788
Other comprehensive income (loss) before reclassifications	0	0
Less: Amounts reclassified from accumulated other comprehensive loss	(23)	478
Net current-period other comprehensive income (loss)	(23)	478
Ending Balance	934	1,266
Net change in fair value of derivative used for cash flow hedge
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(1,772)	0
Other comprehensive income (loss) before reclassifications	(112)	0
Less: Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income (loss)	(112)	0
Ending Balance	(1,884)	0
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7,617)	696
Other comprehensive income (loss) before reclassifications	1,160	10,572
Less: Amounts reclassified from accumulated other comprehensive loss	(330)	186
Net current-period other comprehensive income (loss)	830	10,758
Ending Balance	$ (6,787)	$ 11,454