Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Unrealized gain on securities, before tax amount	$ (34,991)	$ 6,575
Unrealized gain on securities, tax effect	7,347	(2,302)
Unrealized gain on securities, net of tax amount	(27,644)	4,273
Reclassification adjustment for securities gains included in net income, before tax amount	(19)	(1,106)
Reclassification adjustment for securities gains included in net income, tax effect	3	387
Reclassification adjustment for securities gains included in net income, net of tax amount	(16)	(719)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, before tax amount	285
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, tax effect	(61)
Non-credit related unrealized gains on other-than-temporarily impaired debt securities, net of tax amount	(224)	0
Amortization of net unrecognized pension and postretirement items, before tax amount	430	528
Amortization of net unrecognized pension and postretirement items, tax effect	(91)	(185)
Amortization of net unrecognized pension and postretirement items, net of tax amount	339	343
Total Other Comprehensive Income, Before Tax Amount	(34,295)	5,997
Total Other Comprehensive Income, Tax Effect	7,198	(2,100)
Other Comprehensive (Loss) Income	$ (27,097)	$ 3,897