Stockholders' Equity (Accumulated Other Comprehensive (Loss) Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified out of accumulated other comprehensive loss per ASU 2016-01 (a)	$ (5,020)
Other Comprehensive Income (Loss), Reclassification Adjustment in Net Income, Net of Tax	1
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,218		$ 1,129
Accumulated Other Comprehensive (Loss) Income [Roll Forward]
Unrealized Loss on Securities	(2,088)
Realized gain on sale of securities, net of tax	(1)
Other comprehensive (loss) income, net of reclassifications and tax	(6,935)
Unrealized Loss on Securities	(14,044)
Unrecognized Net Pension and Postretirement Costs	4,256
Other comprehensive (loss) income, net of reclassifications and tax	20
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	1,089	$ (67)
Unrecognized Net Pension and Postretirement Costs	(4,236)
Accumulated Other Comprehensive Loss	(5,215)
Other comprehensive (loss) income, net of reclassifications and tax	(5,826)
Accumulated Other Comprehensive Loss	$ (16,062)