Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ 11,832	$ (10,400)	$ (3,226)
Total other comprehensive income (loss), tax expense (benefit)	4,393	(4,031)	(1,289)
Other comprehensive income (loss), net of tax	7,439	(6,369)	(1,937)
Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	(3,617)	(10,119)	(571)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	(1,399)	(3,913)	(220)
Other comprehensive income (loss), before reclassifications, net of tax	(2,218)	(6,206)	(351)
Reclassification from AOCI, pre-tax	(148)	(1,186)	(96)
Reclassification from AOCI, tax expense (benefit)	(57)	(459)	(37)
Reclassification from AOCI, net of tax	(91)	(727)	(59)
Total other comprehensive income (loss), pre-tax	9,172	(11,404)	(845)
Total other comprehensive income (loss), tax expense (benefit)	3,546	(4,410)	(325)
Other comprehensive income (loss), net of tax	5,626	(6,994)	(520)
Accumulated Net Investment Gain (Loss) Attributable to Parent, Securities Transferred from Held to Maturity to Available for Sale [Member]
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
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)	(178)
Reclassification from AOCI, tax expense (benefit)	(109)	(38)	(68)
Reclassification from AOCI, net of tax	(173)	(61)	(110)
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	874	856	(420)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	338	329	(171)
Other comprehensive income (loss), before reclassifications, net of tax	536	527	(249)
Total other comprehensive income (loss), pre-tax	874	856	(420)
Total other comprehensive income (loss), tax expense (benefit)	338	329	(171)
Other comprehensive income (loss), net of tax	536	527	(249)
Defined benefit Pension and Post-Retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax		480
Reclassification from AOCI, tax expense (benefit)		178
Reclassification from AOCI, net of tax		302
Total other comprehensive income (loss), pre-tax	1,786	148	(1,961)
Total other comprehensive income (loss), tax expense (benefit)	509	50	(793)
Other comprehensive income (loss), net of tax	1,277	98	(1,168)
Net gain (losses) arising during the period
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, pre-tax	1,379	51	(2,393)
Other comprehensive income (loss) before reclassifications, tax expense (benefit)	351	20	(958)
Other comprehensive income (loss), before reclassifications, net of tax	1,028	31	(1,435)
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)
Amortization of net actuarial loss recognized in net periodic pension cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, pre-tax	407		432
Reclassification from AOCI, tax expense (benefit)	158		165
Reclassification from AOCI, net of tax	$ 249		$ 267