Accumulated Other Comrehensive Loss (Components of AOCI) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (135,192)	$ (64,440)
Other comprehensive (loss) income before reclassifications		9,479	(58,401)
Amounts reclassified from accumulated other comprehensive loss	[1]	3,419	(12,351)
Net current period other comprehensive income (loss)		12,898	(70,752)	$ (11,459)
Ending balance		(122,294)	(135,192)	(64,440)
Unrealized Loss on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]	0	(892)
Other comprehensive (loss) income before reclassifications	[2]	0	892
Amounts reclassified from accumulated other comprehensive loss	[2]	0	0
Net current period other comprehensive income (loss)	[2]	0	892
Ending balance	[2]	0	0	(892)
Unrealized Gains on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]	(45,875)	(15,125)
Other comprehensive (loss) income before reclassifications	[2]	17,635	(13,946)
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	(2,705)	(16,804)
Net current period other comprehensive income (loss)	[2]	14,930	(30,750)
Ending balance	[2]	(30,945)	(45,875)	(15,125)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]	(89,317)	(48,423)
Other comprehensive (loss) income before reclassifications	[2]	(8,156)	(45,347)
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	6,124	4,453
Net current period other comprehensive income (loss)	[2]	(2,032)	(40,894)
Ending balance	[2]	$ (91,349)	$ (89,317)	$ (48,423)

[1] Amounts in parentheses indicate debits to profit/loss.

[2] All amounts are net of tax. Amounts in parentheses indicate debits.