Other Comprehensive Income (Loss) - Changes in the Components of Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ (5,594)	$ 12,230	$ (18,394)	$ 21,092
Total other comprehensive income (loss), tax expense (benefit)	(1,423)	4,728	(4,682)	8,154
Other comprehensive (loss) income, net of tax	(4,171)	7,502	(13,712)	12,938
Securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	(6,548)		(21,182)	7,739
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	(1,666)		(5,391)	2,992
Other comprehensive income (loss), before reclassifications, net of tax	(4,882)		(15,791)	4,747
Reclassification from AOCI, pre-tax	15		15
Reclassification from AOCI, tax expense (benefit)	4		4
Reclassification from AOCI, net of tax	11		11
Total other comprehensive income (loss), pre-tax	(6,533)	11,966	(21,167)	20,618
Total other comprehensive income (loss), tax expense (benefit)	(1,662)	4,626	(5,387)	7,971
Other comprehensive (loss) income, net of tax	(4,871)	7,340	(15,780)	12,647
Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	857	163	2,527	169
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	218	63	643	65
Other comprehensive income (loss), before reclassifications, net of tax	639	100	1,884	104
Total other comprehensive income (loss), pre-tax	857	163	2,527	169
Total other comprehensive income (loss), tax expense (benefit)	218	63	643	65
Other comprehensive (loss) income, net of tax	639	100	1,884	104
Amortization of net actuarial loss recognized in net periodic pension cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax	82	101	246	305
Reclassification from AOCI, tax expense (benefit)	21	39	62	118
Reclassification from AOCI, net of tax	61	62	184	187
Defined benefit Pension and Post-Retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	82	101	246	305
Total other comprehensive income (loss), tax expense (benefit)	21	39	62	118
Other comprehensive (loss) income, net of tax	$ 61	62	$ 184	187
Securities available for sale, transferred from HTM to AFS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax		13,218		13,218
Other comprehensive income (loss) before reclassifications, tax expense (benefit)		5,110		5,110
Other comprehensive income (loss), before reclassifications, net of tax		8,108		8,108
Unrealized holding losses on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax		(1,188)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)		(459)
Other comprehensive income (loss), before reclassifications, net of tax		(729)
Reclassification adjustment for gains realized in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax		(57)		(57)
Reclassification from AOCI, tax expense (benefit)		(22)		(22)
Reclassification from AOCI, net of tax		(35)		(35)
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		(7)		(282)
Reclassification from AOCI, tax expense (benefit)		(3)		(109)
Reclassification from AOCI, net of tax		$ (4)		$ (173)