Other Comprehensive Income - Changes in Components of OCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ (9,908)	$ 11,832	$ (10,400)
Total other comprehensive income (loss), tax expense (benefit)	(2,523)	4,393	(4,031)
Other comprehensive (loss) income, net of tax	(7,385)	7,439	(6,369)
Unrealized holding losses on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax		(3,617)	(10,119)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)		(1,399)	(3,913)
Other comprehensive income (loss), before reclassifications, net of tax		(2,218)	(6,206)
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		(148)	(1,186)
Reclassification from AOCI, tax expense (benefit)		(57)	(459)
Reclassification from AOCI, net of tax		(91)	(727)
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)	(99)
Reclassification from AOCI, tax expense (benefit)		(109)	(38)
Reclassification from AOCI, net of tax		(173)	(61)
Total securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	(11,155)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	(2,840)
Other comprehensive income (loss), before reclassifications, net of tax	(8,315)
Reclassification from AOCI, pre-tax	16
Reclassification from AOCI, tax expense (benefit)	4
Reclassification from AOCI, net of tax	12
Total other comprehensive income (loss), pre-tax	(11,139)	9,172	(11,404)
Total other comprehensive income (loss), tax expense (benefit)	(2,836)	3,546	(4,410)
Other comprehensive (loss) income, net of tax	(8,303)	5,626	(6,994)
Total derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	490	874	856
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	125	338	329
Other comprehensive income (loss), before reclassifications, net of tax	365	536	527
Total other comprehensive income (loss), pre-tax	490	874	856
Total other comprehensive income (loss), tax expense (benefit)	125	338	329
Other comprehensive (loss) income, net of tax	365	536	527
Net gain arising during the period
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	413	1,379	51
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	105	351	20
Other comprehensive income (loss), before reclassifications, net of tax	308	1,028	31
Amortization of net actuarial loss recognized in net periodic pension cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax	328	407	480
Reclassification from AOCI, tax expense (benefit)	83	158	178
Reclassification from AOCI, net of tax	245	249	302
Reclassification of adjustment for net settlement gain realized in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax			(383)
Reclassification from AOCI, tax expense (benefit)			(148)
Reclassification from AOCI, net of tax			(235)
Total defined benefit pension and post-retirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	741	1,786	148
Total other comprehensive income (loss), tax expense (benefit)	188	509	50
Other comprehensive (loss) income, net of tax	$ 553	$ 1,277	$ 98