Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gain on securities, before tax amount	$ 23,150	$ (15,865)	$ 81,207	$ (59,250)
Unrealized gain on securities, tax effect	(5,121)	3,334	(17,963)	12,444
Unrealized gain on securities, net of tax amount	18,029	(12,531)	63,244	(46,806)
Reclassification adjustment for securities gains included in net income, before tax amount	(4,492)	(14)	(4,733)	(37)
Reclassification adjustment for securities gains included in net income, tax effect	994	3	1,047	7
Reclassification adjustment for securities gains included in net income, net of tax amount	(3,498)	(11)	(3,686)	(30)
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	4,405	1,000		1,000
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	(974)	(209)		(209)
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	3,430	791	5,425	791
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Investment Transferred From Available-For-Sale To Held-To-Maturity, Before Tax			6,966
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Investment Transferred From Available-For-Sale To Held-To-Maturity, Tax			(1,541)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Investment Transferred from Available-for-sale to Held-to-maturity, after Tax			5,425
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, before tax amount			(875)	294
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, tax effect			193	(62)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, net of tax amount	0	0	(682)	232
Amortization of net unrecognized pension and postretirement items, before tax amount	357	466	1,083	1,580
Amortization of net unrecognized pension and postretirement items, tax effect	(80)	(97)	(240)	(332)
Amortization of net unrecognized pension and postretirement items, net of tax amount	277	369	843	1,248
Total Other Comprehensive Income, Before Tax Amount	23,419	(14,413)	83,648	(56,413)
Total Other Comprehensive Income, Tax Effect	(5,181)	3,031	(18,504)	11,848
Other Comprehensive Income (Loss)	$ 18,238	$ (11,382)	65,144	$ (44,565)
Accounting Standards Update 2019-04 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Investment Transferred From Available-For-Sale To Held-To-Maturity, Before Tax			$ 3,700