Shareholders' Equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Before-Tax Amount
Unrealized gain on securities	$ 85,188	$ 73,085	$ (31,235)
Reclassification adjustment for securities gains included in net income	(3,053)	(4,733)	(37)
Amortization of net unrealized losses on available for sale securities transferred to held to maturity	4,360	8,070	2,694
Non-credit related unrealized losses on other-than-temporarily impaired debt securities		(873)	285
Unrecognized pension and postretirement income	(3,242)	(1,203)	1,798
Amortization of net unrecognized pension and postretirement income	1,311	1,316	2,116
Total Other Comprehensive Income	84,564	75,662	(24,379)
Tax Effect
Unrealized gain on securities	(19,537)	(16,166)	6,909
Reclassification adjustment for securities gains included in net income	694	1,047	7
Amortization of net unrealized losses on available for sale securities transferred to held to maturity	(912)	(1,785)	(596)
Non-credit related unrealized losses on other-than-temporarily impaired debt securities		193	(63)
Unrecognized pension and postretirement income (cost)	710	266	(398)
Amortization of net unrecognized pension and postretirement income	(291)	(291)	(468)
Total Other Comprehensive Income	(19,336)	(16,736)	5,391
Other Comprehensive Income (Loss), net of tax:
Unrealized gain on securities	65,651	56,919	(24,326)
Reclassification adjustment for securities gains included in net income	(2,359)	(3,686)	(30)
Amortization of net unrealized losses on available for sale securities transferred to held to maturity	3,448	6,285	2,098
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, Net of Tax, Portion Attributable to Parent	0	(680)	222
Unrecognized pension and postretirement income	(2,532)	(937)	1,400
Amortization of net unrecognized pension and postretirement income	1,020	1,025	1,648
Total Other Comprehensive Income	65,228	$ 58,926	$ (18,988)
Accounting Standards Update 2019-04
Before-Tax Amount
Amortization of net unrealized losses on available for sale securities transferred to held to maturity	$ 3,700