Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Unrealized gain on securities, before tax amount	$ 31,994	$ (8,397)	$ 58,056	$ (43,388)
Unrealized gain on securities, tax effect	(7,077)	1,766	(12,841)	9,113
Unrealized gain on securities, net of tax amount	24,917	(6,631)	45,215	(34,275)
Reclassification adjustment for securities gains included in net income, before tax amount	(176)	(4)	(241)	(23)
Reclassification adjustment for securities gains included in net income, tax effect	39	1	53	4
Reclassification adjustment for securities gains included in net income, net of tax amount	(137)	(3)	(188)	(19)
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	1,311
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	(290)
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	1,021	0	1,995	0
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Investment Transferred From Available-For-Sale To Held-To-Maturity, Before Tax			2,563
Other Comprehensive Income (Loss), Reclassification Adjustment From AOCI For Investment Transferred From Available-For-Sale To Held-To-Maturity, Tax			(568)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Investment Transferred from Available-for-sale to Held-to-maturity, after Tax			1,995
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, before tax amount	(770)	9	(875)	294
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, tax effect	170	(1)	193	(62)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, net of tax amount	(600)	8	(682)	232
Amortization of net unrecognized pension and postretirement items, before tax amount	353	683	727	1,113
Amortization of net unrecognized pension and postretirement items, tax effect	(78)	(143)	(161)	(234)
Amortization of net unrecognized pension and postretirement items, net of tax amount	275	540	566	879
Total Other Comprehensive Income, Before Tax Amount	32,712	(7,709)	60,230	(42,004)
Total Other Comprehensive Income, Tax Effect	(7,236)	1,623	(13,324)	8,821
Other Comprehensive Income (Loss)	$ 25,476	$ (6,086)	$ 46,906	$ (33,183)