Other Comprehensive Income/Loss - Components of Other Comprehensive Income/Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Before Tax Amount	$ (53)	$ 7,402
Income Tax Benefit (Expense)	21	(2,992)
Total other comprehensive (loss) income, net of tax	(32)	4,410
Net unrealized gain (loss) on securities available-for-sale
Other Comprehensive Income (Loss), Before Reclassifications [Abstract]
Before Tax Amount	(724)	6,774
Income Tax Benefit (Expense)	292	(2,738)
After Tax Amount	(432)	4,036
Other Comprehensive Income (Loss), Reclassifications Adjustments [Abstract]
Before Tax Amount		(86)
Income Tax Benefit (Expense)		35
After Tax Amount		(51)
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Before Tax Amount		6,688
Income Tax Benefit (Expense)		(2,703)
Total other comprehensive (loss) income, net of tax	(432)	3,985
Reclassification adjustment for net actuarial loss on pension plans and other postretirement benefits included in net income
Other Comprehensive Income (Loss), Reclassifications Adjustments [Abstract]
Before Tax Amount	623	667
Income Tax Benefit (Expense)	(252)	(270)
After Tax Amount	371	397
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Total other comprehensive (loss) income, net of tax	371	397
Reclassification adjustment for prior service cost on pension plans and other postretirement benefits included in net income
Other Comprehensive Income (Loss), Reclassifications Adjustments [Abstract]
Before Tax Amount	48	47
Income Tax Benefit (Expense)	(19)	(19)
After Tax Amount	29	28
Other Comprehensive Income (Loss), After Reclassification Adjustments [Abstract]
Total other comprehensive (loss) income, net of tax	$ 29	$ 28