Accumulated Other Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Other income - net realized gains on sales of available for sale securities	$ 598	$ 997
Interest expense - subordinated debentures and term loans	1,817	1,785
Amortization of prior service costs	25,732	27,337
Income tax expense	(7,168)	(5,574)
Total reclassifications for the period, net of tax	274	437
Unrealized gains (losses) on available for sale securities
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period, net of tax	389	648
Unrealized gains (losses) on cash flow hedges
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period, net of tax	(174)	(211)
Unrealized Gains (Losses) on Defined Benefit Plans
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period, net of tax	59
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) for the Period | Unrealized gains (losses) on available for sale securities
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Other income - net realized gains on sales of available for sale securities	598	997
Income tax expense	(209)	(349)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) for the Period | Unrealized gains (losses) on cash flow hedges
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	94	113
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) for the Period | Unrealized gains (losses) on cash flow hedges | Interest rate contracts
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Interest expense - subordinated debentures and term loans	(268)	(324)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) for the Period | Unrealized Gains (Losses) on Defined Benefit Plans
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service costs	91
Income tax expense	(32)
Total reclassifications for the period, net of tax	$ 59	$ 0