Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net change in unrealized gains (losses), tax expense (benefit)	$ 1,813	$ (2,968)	$ (868)
Reclassification adjustment for gains, tax expense	704	900	562
Amortization of unrealized gain on securities reclassified to held-to-maturity, tax expense	241	248	234
Change in unfunded pension liability related to unrealized (loss) gain, prior service cost and transition obligation, tax (benefit) expense	(56)	103	(37)
Net change in cash flow hedge, tax (benefit)	$ (113)	$ (1,086)	$ 0