Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	$ 515,630	$ 501,718	$ 489,871	$ 470,815	$ 462,097	$ 458,308	$ 489,871	$ 458,308
Other comprehensive income (loss) - before reclassifications	1,790			(3,010)			10,499	(9,556)
Amount reclassified from accumulated other comprehensive income	(87)			(194)			(261)	(1,638)
Other comprehensive income (loss), net of tax	1,703	5,237	3,298	(3,204)	(1,306)	(5,338)	10,238	(9,848)
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect				(1,346)	(1,346)			(1,346)	$ 0
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect						0
Tax Cuts and Jobs Act of 2017, Other comprehensive income (loss), Tax Effect				0				0
Balance	526,163	515,630	501,718	477,118	470,815	462,097	526,163	477,118
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(1,774)	(7,011)	(10,309)	(9,796)	(8,490)	(1,806)	(10,309)	(1,806)
Other comprehensive income (loss), net of tax	1,703	5,237	3,298	(3,204)	(1,306)	(5,338)
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect				0		(1,346)		(1,346)
Balance	(71)	(1,774)	(7,011)	(13,000)	(9,796)	(8,490)	(71)	(13,000)
Net Unrealized Holding Gain (Loss) on Securities Available for Sale, Net of Tax [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(1,707)		(10,416)	(11,576)		(5,030)	(10,416)	(5,030)
Other comprehensive income (loss) - before reclassifications	1,790			(3,010)			10,499	(9,556)
Amount reclassified from accumulated other comprehensive income	0			0			0	0
Other comprehensive income (loss), net of tax	1,790			(3,010)			10,499	(9,556)
Balance	83	(1,707)		(14,586)	(11,576)		83	(14,586)
Net Change in Overfunded Position in Pension and Postretirement Plans Arising During the Year, Net of Tax [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	423		423				423
Other comprehensive income (loss) - before reclassifications	0						0
Amount reclassified from accumulated other comprehensive income	0						0
Other comprehensive income (loss), net of tax	0						0
Balance	423	423					423
Net Change in Net Actuarial (Gain) Loss and Prior Service Credit/Cost on Pension and Postretirement Benefit Plans, Net of Tax [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(490)		$ (316)	3,126		$ 3,224	(316)	3,224
Other comprehensive income (loss) - before reclassifications	0			0			0	0
Amount reclassified from accumulated other comprehensive income	(87)			(194)			(261)	(292)
Other comprehensive income (loss), net of tax	(87)			(194)			(261)	(292)
Balance	$ (577)	$ (490)		$ 2,932	$ 3,126		$ (577)	$ 2,932