Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gain on securities, before tax amount	$ 5,565	$ 23,150	$ 72,146	$ 81,207
Unrealized gain on securities, tax effect	(1,232)	(5,121)	(15,960)	(17,963)
Unrealized gain on securities, net of tax amount	4,333	18,029	56,186	63,244
Reclassification adjustment for securities gains included in net income, before tax amount	(2)	(4,492)	(3,053)	(4,733)
Reclassification adjustment for securities gains included in net income, tax effect	1	994	676	1,047
Reclassification adjustment for securities gains included in net income, net of tax amount	(1)	(3,498)	(2,377)	(3,686)
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Amortization Of Unrealized Losses On Investments Transferred From Available-For-Sale To Held-To-Maturity, Before Tax	1,192	4,405	3,232	6,966
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Amortization Of Unrealized Losses On Investments Transferred From Available-For-Sale To Held-To-Maturity, Tax	(264)	(974)	(715)	(1,541)
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Amortization Of Unrealized Losses On Investments Transferred From Available-For-Sale To Held-To Maturity, After Tax	928	3,430	2,517	5,425
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, before tax amount				(875)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, tax effect				193
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, net of tax amount	0	0	0	(682)
Amortization of net unrecognized pension and postretirement items, before tax amount	329	357	984	1,083
Amortization of net unrecognized pension and postretirement items, tax effect	(73)	(80)	(219)	(240)
Amortization of net unrecognized pension and postretirement items, net of tax amount	255	277	765	843
Total Other Comprehensive Income, Before Tax Amount	7,083	23,419	73,309	83,648
Total Other Comprehensive Income, Tax Effect	(1,568)	(5,181)	(16,218)	(18,504)
Other Comprehensive Income	$ 5,515	$ 18,238	$ 57,091	65,144
Accounting Standards Update 2019-04
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Transfers From Available-For-Sale To Held-To-Maturity Securities, Before Tax				$ 3,700