Shareholders' Equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Before-Tax Amount
Unrealized loss on securities	$ (22,907)	$ (11,872)	$ 51,901
Reclassification adjustment for securities gains included in net income (1)	(2,550)	(9,066)	(2,041)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax		3,778
Non-credit related unrealized loss on other-than-temporarily impaired debt securities	(285)	368	1,200
Amortization of unrealized loss on derivative financial instruments (2)	25	115	209
Unrecognized pension and postretirement cost	(1,432)	7,200	(20,258)
Amortization of net unrecognized pension and postretirement items (3)	1,869	2,869	627
Total Other Comprehensive Loss	(25,280)	(6,608)	30,186
Tax Effect
Unrealized loss on securities	8,016	4,155	(18,167)
Reclassification adjustment for securities gains included in net income (1)	893	3,174	714
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax		(1,322)
Non-credit related unrealized loss on other-than-temporarily impaired debt securities	100	(129)	(420)
Amortization of unrealized loss on derivative financial instruments (2)	(9)	(40)	(73)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax			(508)
Unrecognized pension and postretirement cost	501	(2,520)	7,090
Amortization of net unrecognized pension and postretirement items (3)	(653)	(1,005)	(219)
Total Other Comprehensive Loss	8,848	2,313	(10,567)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax			(944)
Net of Tax Amount
Unrealized loss on securities	(14,891)	(7,717)	33,734
Reclassification adjustment for securities gains included in net income (1)	(1,657)	(5,892)	(1,327)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	2,456	0
Non-credit related unrealized loss on other-than-temporarily impaired debt securities	(185)	239	780
Amortization of unrealized loss on derivative financial instruments (2)	16	75	136
Unrecognized pension and postretirement cost	(931)	4,680	(13,168)
Amortization of net unrecognized pension and postretirement items (3)	1,216	1,864	408
Total Other Comprehensive Loss	$ (16,432)	$ (4,295)	19,619
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax			$ (1,452)