Accumulated Other Comprehensive Income Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Unrealized gain on securities, before tax amount	$ 5,109	$ (5,505)	$ 27,482	$ 40,441
Unrealized gain on securities, tax effect	(1,789)	1,925	(9,621)	(14,156)
Unrealized gain on securities, net of tax amount	3,320	(3,580)	17,861	26,285
Reclassification adjustment for securities gains included in net income, before tax amount	(4,597)	(2)	(7,139)	(1,025)
Reclassification adjustment for securities gains included in net income, tax effect	1,609	1	2,500	359
Reclassification adjustment for securities gains included in net income, net of tax amount	(2,988)	(1)	(4,639)	(666)
Amortization of unrealized loss on derivative financial instruments, before tax amount		6		18
Amortization of unrealized loss on derivative financial instruments, tax effect		(2)		(6)
Amortization of unrealized loss on derivative financial instruments, net of tax amount	0	4	0	12
Amortization of net unrecognized pension and postretirement items, before tax amount	523	583	1,575	1,349
Amortization of net unrecognized pension and postretirement items, tax effect	(183)	(204)	(551)	(472)
Amortization of net unrecognized pension and postretirement items, net of tax amount	340	379	1,024	877
Total Other Comprehensive Income, Before Tax Amount	1,035	(4,918)	21,918	40,783
Total Other Comprehensive Income, Tax Effect	(363)	1,720	(7,672)	(14,275)
Other Comprehensive Income (Loss)	$ 672	$ (3,198)	$ 14,246	$ 26,508