Other Comprehensive Income - Changes in Components of OCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ 25,029	$ (9,908)	$ 11,832
Total other comprehensive income (loss), tax expense (benefit)	6,369	(2,523)	4,393
Other comprehensive income (loss), net of tax	18,660	(7,385)	7,439
Total securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	24,983
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	6,358
Other comprehensive income (loss), before reclassifications, net of tax	18,625
Reclassification from AOCI, pre-tax	2,511
Reclassification from AOCI, tax expense (benefit)	639
Reclassification from AOCI, net of tax	1,872
Total other comprehensive income (loss), pre-tax	27,494	(11,139)	9,172
Total other comprehensive income (loss), tax expense (benefit)	6,997	(2,836)	3,546
Other comprehensive income (loss), net of tax	20,497	(8,303)	5,626
Total derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	(2,975)	490	874
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	(758)	125	338
Other comprehensive income (loss), before reclassifications, net of tax	(2,217)	365	536
Total other comprehensive income (loss), pre-tax	(2,975)	490	874
Total other comprehensive income (loss), tax expense (benefit)	(758)	125	338
Other comprehensive income (loss), net of tax	(2,217)	365	536
Net gain arising during the period
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	91	413	1,379
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	23	105	351
Other comprehensive income (loss), before reclassifications, net of tax	68	308	1,028
Amortization of net actuarial loss recognized in net periodic pension cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax	419	328	407
Reclassification from AOCI, tax expense (benefit)	107	83	158
Reclassification from AOCI, net of tax	312	245	249
Total defined benefit pension and post-retirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	510	741	1,786
Total other comprehensive income (loss), tax expense (benefit)	130	188	509
Other comprehensive income (loss), net of tax	$ 380	553	1,277
Unrealized holding losses on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax		(11,155)	(3,617)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)		(2,840)	(1,399)
Other comprehensive income (loss), before reclassifications, net of tax		(8,315)	(2,218)
Unrealized holding gains on securities transferred from held to maturity to available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax			13,219
Other comprehensive income (loss) before reclassifications, tax expense (benefit)			5,111
Other comprehensive income (loss), before reclassifications, net of tax			8,108
Reclassification adjustment for gains realized in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax		16	(148)
Reclassification from AOCI, tax expense (benefit)		4	(57)
Reclassification from AOCI, net of tax		$ 12	(91)
Amortization of unrealized holding gains on securities transferred to the held to maturity category
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax			(282)
Reclassification from AOCI, tax expense (benefit)			(109)
Reclassification from AOCI, net of tax			$ (173)