Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 31,157	$ 10,941	$ 16,684
Available-for-sale investment securities:
Gross unrealized holding (loss) gain arising in the period	(2,590)	1,232	19,326
Related tax benefit (expense)	906	(431)	(6,764)
Less: reclassification adjustment for net gain included in net income	930	729	398
Related tax expense	(326)	(255)	(139)
Net effect on other comprehensive (loss) income	(2,288)	327	12,303
Defined benefit plans:
Net (loss) gain arising during the period	(232)	373	(2,083)
Related tax benefit (expense)	81	(130)	729
Amortization of unrecognized loss and service cost on benefit plans	89	112	129
Related tax expense	(31)	(38)	(45)
Recognition of loss due to settlement and curtailment	0	459	1,400
Related tax expense	0	(161)	(490)
Net effect on other comprehensive (loss) income	(93)	615	(360)
Net gain arising during the period	1,824	0	0
Related tax expense	(638)	0	0
Net effect on other comprehensive income	1,186	0	0
Total other comprehensive (loss) income, net of tax	(1,195)	942	11,943
Total comprehensive income	$ 29,962	$ 11,883	$ 28,627