Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Unrealized gain on securities, before tax amount	$ (8,397)	$ 15,798	$ (43,388)	$ 22,374
Unrealized gain on securities, tax effect	1,766	(5,530)	9,113	(7,833)
Unrealized gain on securities, net of tax amount	(6,631)	10,268	(34,275)	14,541
Reclassification adjustment for securities gains included in net income, before tax amount	(4)	(1,436)	(23)	(2,542)
Reclassification adjustment for securities gains included in net income, tax effect	1	504	4	891
Reclassification adjustment for securities gains included in net income, net of tax amount	(3)	(932)	(19)	(1,651)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, before tax amount	9		294
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, tax effect	(1)		(62)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, net of tax amount	(8)	0	(232)	0
Amortization of net unrecognized pension and postretirement items, before tax amount	683	522	1,113	1,051
Amortization of net unrecognized pension and postretirement items, tax effect	(143)	(181)	(234)	(367)
Amortization of net unrecognized pension and postretirement items, net of tax amount	540	341	879	684
Total Other Comprehensive Income, Before Tax Amount	(7,709)	14,884	(42,004)	20,883
Total Other Comprehensive Income, Tax Effect	1,623	(5,207)	8,821	(7,309)
Other Comprehensive (Loss) Income	$ (6,086)	$ 9,677	$ (33,183)	$ 13,574