Other Comprehensive Income (Loss) - Tax effects of components in other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Components of other comprehensive income (loss), Before Tax
Unrealized gains and losses on debt securities available for sale:	$ 11,766	$ (11,594)
Accretion of unrealized gain (loss) on debt securities reclassified as held to maturity	13	(17)
Reclassification adjustment for gains included in net income	126	116
Total other comprehensive (loss) income, before tax	11,905	(11,495)
Unrealized (loss) gain on swap contracts	(3,520)
Unrealized (loss) gain on swap contracts		382
Employee benefit plans, Before tax
Amortization of prior service cost included in net income	(32)	(24)
Reclassification adjustment of actuarial net gain (loss) included in net income	164	(8)
Change in funded status of retirement obligations	(132)	33
Total employee benefit plans, before tax	0	1
Total other comprehensive income (loss)	8,385	(11,112)
Components of other comprehensive income (loss), Tax Effect
Unrealized gains and losses on debt securities available for sale:	(2,471)	1,609
Accretion of unrealized gain (loss) on debt securities reclassified as held to maturity	(3)	36
Reclassification adjustment for gains included in net income	(26)	(28)
Total other comprehensive (loss) income, tax	(2,500)	1,617
Unrealized (loss) gain on swap contracts	740
Unrealized (loss) gain on swap contracts		(40)
Employee benefit plans, Tax Effect
Amortization of prior service cost included in net income	7	(19)
Reclassification adjustment of actuarial net gain (loss) included in net income	(34)	(94)
Change in funded status of retirement obligations	27	(301)
Total employee benefit plans, tax	0	(414)
Total other comprehensive income (loss)	(1,760)	1,163
Components of other comprehensive income (loss), After Tax
Unrealized gains and losses on debt securities available for sale:	9,295	(9,985)
Accretion of unrealized gain on debt securities reclassified as held to maturity	10	19
Reclassification adjustment for gains included in net income	100	88
Total other comprehensive (loss) income, net of tax	9,405	(9,878)
Unrealized (loss) gain on swap contracts	(2,780)
Unrealized gain (loss) on swap contract, Net of tax		342
Employee benefit plans, After Tax
Amortization of prior service cost included in net income	(25)	(43)
Reclassification adjustment of actuarial net gain (loss) included in net income	130	(102)
Change in funded status of retirement obligations	(105)	(268)
Total employee benefit plans, net of tax	0	(413)
Total other comprehensive income (loss)	$ 6,625	$ (9,949)