Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity [Abstract]
Unrealized gain on securities, before tax amount	$ 15,798	$ 19,753	$ 22,374	$ 45,946
Unrealized gain on securities, tax effect	(5,530)	(6,914)	(7,833)	(16,081)
Unrealized gain on securities, net of tax amount	10,268	12,839	14,541	29,865
Reclassification adjustment for securities gains included in net income, before tax amount	(1,436)	(76)	(2,542)	(1,023)
Reclassification adjustment for securities gains included in net income, tax effect	504	27	891	358
Reclassification adjustment for securities gains included in net income, net of tax amount	(932)	(49)	(1,651)	(665)
Amortization of unrealized loss on derivative financial instruments, before tax amount		6		12
Amortization of unrealized loss on derivative financial instruments, tax effect		(2)		(4)
Amortization of unrealized loss on derivative financial instruments, net of tax amount	0	4	0	8
Amortization of net unrecognized pension and postretirement items, before tax amount	522	49	1,051	766
Amortization of net unrecognized pension and postretirement items, tax effect	(181)	(17)	(367)	(268)
Amortization of net unrecognized pension and postretirement items, net of tax amount	341	32	684	498
Total Other Comprehensive Income, Before Tax Amount	14,884	19,732	20,883	45,701
Total Other Comprehensive Income, Tax Effect	(5,207)	(6,906)	(7,309)	(15,995)
Other Comprehensive Income	$ 9,677	$ 12,826	$ 13,574	$ 29,706