Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AFS Securities:
Unrealized holdings losses, pre-tax amount	$ 26,743	$ (10,846)	$ (2,905)
Unrealized holdings losses, tax (expense) benefit	(5,750)	2,332	1,017
Unrealized holdings losses, after-tax amount	20,993	(8,514)	(1,888)
Less: reclassification adjustment for realized losses, pre-tax amount	(105)	(663)	855
Less: reclassification adjustment for realized losses, tax (expense) benefit	22	142	(299)
Less: reclassification adjustment for realized losses, after-tax amount	(83)	(521)	556
Net unrealized losses, pre-tax amount	26,848	(10,183)	(3,760)
Net unrealized losses, tax (expense) benefit	(5,772)	2,190	1,316
Net unrealized losses, after-tax amount	21,076	(7,993)	(2,444)
Cash Flow Hedges:
Net increase in fair value, pre-tax amount	(2,973)	1,066	(382)
Net increase in fair value, tax (expense) benefit	639	(229)	134
Net increase in fair value, after-tax amount	(2,334)	837	(248)
Less: effective portion reclassified into interest expense, pre-tax amount	(921)	(831)	(1,592)
Less: effective portion reclassified into interest expense, tax (expense) benefit	198	179	557
Less: effective portion reclassified into interest expense, after-tax amount	(723)	(652)	(1,035)
Net increase in fair value, pre-tax amount	(2,052)	1,897	1,210
Net increase in fair value, tax (expense) benefit	441	(408)	(423)
Net increase in fair value, after-tax amount	(1,611)	1,489	787
Postretirement Plans:
Net actuarial loss, pre-tax amount	(1,918)	1,743	(2,065)
Net actuarial loss, tax (expense) benefit	412	(375)	723
Net actuarial loss, after-tax amount	(1,506)	1,368	(1,342)
Less: Amortization of net actuarial losses, pre-tax amount	(271)	(613)	(286)
Less: Amortization of net actuarial losses, tax (expense) benefit	59	131	100
Less: Amortization of net prior service credits, after-tax amount	(212)	(482)	(186)
Less: Amortization of net prior service credits, pre-tax amount	24	24	24
Less: Amortization of net prior service credits, tax (expense) benefit	(5)	(5)	(8)
Less: Amortization of net prior service credits, after-tax amount	19	19	16
Net loss on postretirement plans, pre-tax amount	(1,671)	2,332	(1,803)
Net loss on postretirement plans, tax (expense) benefit	358	(501)	631
Net (loss) gain on postretirement plans, net of tax	(1,313)	1,831	(1,172)
Other comprehensive income, pre-tax amount	23,125	(5,954)	(4,353)
Other comprehensive income, tax (expense) benefit	(4,973)	1,281	1,524
Other comprehensive income (loss)	$ 18,152	$ (4,673)	$ (2,829)