Other Comprehensive Income/Loss - Components of Other Comprehensive Income/Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Before Tax Amount	$ 12,308	$ (45,487)	$ 53,714
Tax (Expense) Benefit	(4,974)	17,786	(18,874)
After Tax Amount	7,334	(27,701)	34,840
Net unrealized gain (loss) on securities available-for-sale
Other Comprehensive Income (Loss), Before Reclassifications [Abstract]
Before Tax Amount	(3,048)	14,134	(16,202)
Tax (Expense) Benefit	1,232	(4,991)	5,717
After Tax Amount	(1,816)	9,143	(10,485)
Other Comprehensive Income (Loss), Reclassifications Adjustments [Abstract]
Before Tax Amount	(72)	(141)	(2,057)
Tax (Expense) Benefit	29	50	725
After Tax Amount	(43)	(91)	(1,332)
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Before Tax Amount	(3,120)	13,993	(18,259)
Tax (Expense) Benefit	1,261	(4,941)	6,442
After Tax Amount	(1,859)	9,052	(11,817)
Net actuarial loss on pension plans and other postretirement benefits
Other Comprehensive Income (Loss), Before Reclassifications [Abstract]
Before Tax Amount	12,265	(60,583)	68,150
Tax (Expense) Benefit	(4,956)	23,116	(23,970)
After Tax Amount	7,309	(37,467)	44,180
Other Comprehensive Income (Loss), Reclassifications Adjustments [Abstract]
Before Tax Amount	2,973	913	3,610
Tax (Expense) Benefit	(1,202)	(322)	(1,275)
After Tax Amount	1,771	591	2,335
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Before Tax Amount	15,238	(59,670)	71,760
Tax (Expense) Benefit	(6,158)	22,794	(25,245)
After Tax Amount	9,080	(36,876)	46,515
Prior service cost on pension plans and other postretirement benefits
Other Comprehensive Income (Loss), Reclassifications Adjustments [Abstract]
Before Tax Amount	190	190	213
Tax (Expense) Benefit	(77)	(67)	(71)
After Tax Amount	$ 113	$ 123	$ 142