Stockholders' Equity (Line Items in Consolidated Income Statements Affected by Amounts Reclassified from Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of defined benefit pension and post-retirement items		$ 17,315		$ 17,315
Employee Benefit Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of defined benefit pension and post-retirement items				17,315
Amount Reclassified from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, net of tax	[1]		$ (4,403)	(3,083)
Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Held to Maturity Securities Transferred from AFS [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized net loss on securities transferred to HTM	[1]		(1,680)	(1,749)
Tax effect	[1]		380	657
Net of tax	[1]		(1,300)	(1,092)
Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Employee Benefit Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of defined benefit pension and post-retirement items	[1],[2]		(2,448)	(3,105)
Tax effect	[1]		555	1,114
Net of tax	[1]		(1,893)	$ (1,991)
Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification of unrealized gain on cash flow hedges	[1]		979
Tax effect	[1]		(222)
Net of tax	[1]		757
Amortization of loss on terminated cash flash hedges	[1]		(2,544)
Tax effect	[1]		577
Net of tax	[1]		$ (1,967)

[1] Amounts in parentheses indicate reduction in net income.

[2] These AOCI components are included in the computation of net periodic pension and post-retirement cost that is reported with employee benefits expense (see Note 12 - Retirement Plans for additional details).