Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Equity [Abstract]
Unrealized gain on securities, before tax amount	$ 44,199	$ 31,994	$ 66,581	$ 58,056
Unrealized gain on securities, tax effect	(9,775)	(7,077)	(14,728)	(12,841)
Unrealized gain on securities, net of tax amount	34,424	24,917	51,853	45,215
Reclassification adjustment for securities gains included in net income, before tax amount	(3,005)	(176)	(3,051)	(241)
Reclassification adjustment for securities gains included in net income, tax effect	664	39	675	53
Reclassification adjustment for securities gains included in net income, net of tax amount	(2,341)	(137)	(2,376)	(188)
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	1,019	1,311	2,040	2,563
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	(226)	(290)	(451)	(568)
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	793	1,021	1,589	1,995
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, before tax amount		(770)		(875)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, tax effect		170		193
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, net of tax amount	0	(600)	0	(682)
Amortization of net unrecognized pension and postretirement items, before tax amount	328	353	656	727
Amortization of net unrecognized pension and postretirement items, tax effect	(73)	(78)	(146)	(161)
Amortization of net unrecognized pension and postretirement items, net of tax amount	255	275	510	566
Total Other Comprehensive Income, Before Tax Amount	42,541	32,712	66,226	60,230
Total Other Comprehensive Income, Tax Effect	(9,410)	(7,236)	(14,650)	(13,324)
Other Comprehensive Income	$ 33,131	$ 25,476	$ 51,576	$ 46,906