Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 7,792	$ 4,134	$ 23,749	$ 8,358
Available-for-sale investment securities:
Gross unrealized holding (loss) gain arising in the period	(4,068)	7,171	14,681	9,458
Related tax benefit (expense)	1,424	(2,509)	(5,139)	(3,309)
Less: reclassification adjustment for net (loss) gain included in net income	(1)	62	862	673
Related tax expense	0	(22)	(302)	(236)
Net effect on other comprehensive (loss) income	(2,643)	4,622	8,982	5,712
Defined benefit plans:
Net (loss) gain arising during the period	0	(167)	0	340
Related tax benefit (expense)	0	58	0	(119)
Amortization of unrecognized loss and service cost on benefit plans	21	26	66	88
Related tax expense	(9)	(9)	(22)	(30)
Recognition of loss due to settlement and curtailment	0	82	0	454
Related tax expense	0	(29)	0	(159)
Net effect on other comprehensive income (loss)	12	(39)	44	574
Cash flow hedges:
Net gain (loss) arising during the period	68	0	(184)	0
Related tax (expense) benefit	(24)	0	64	0
Net effect on other comprehensive income (loss)	44	0	(120)	0
Total other comprehensive (loss) income, net of tax expense	(2,587)	4,583	8,906	6,286
Total comprehensive income	$ 5,205	$ 8,717	$ 32,655	$ 14,644