Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (102,843)	$ (15,027)	$ (135,192)	$ (64,440)
Other comprehensive income before reclassifications		9,895	(722)	41,218	57,273
Amounts reclassified from accumulated other comprehensive (loss) income		624	965	1,650	(7,617)
Net current period other comprehensive income		10,519	243	42,868	49,656
Ending balance		(92,324)	(14,784)	(92,324)	(14,784)
Unrealized Loss on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	0	0	0	(892)
Other comprehensive income before reclassifications	[1]	0	0	0	892
Amounts reclassified from accumulated other comprehensive (loss) income	[1]	0	0	0	0
Net current period other comprehensive income	[1]	0	0	0	892
Ending balance	[1]	0	0	0	0
Unrealized Gains on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	(16,648)	31,213	(45,875)	(15,125)
Other comprehensive income before reclassifications	[1]	9,895	(722)	41,218	56,381
Amounts reclassified from accumulated other comprehensive (loss) income	[1]	(842)	(161)	(2,938)	(10,926)
Net current period other comprehensive income	[1]	9,053	(883)	38,280	45,455
Ending balance	[1]	(7,595)	30,330	(7,595)	30,330
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	(86,195)	(46,240)	(89,317)	(48,423)
Other comprehensive income before reclassifications	[1]	0	0	0	0
Amounts reclassified from accumulated other comprehensive (loss) income	[1]	1,466	1,126	4,588	3,309
Net current period other comprehensive income	[1]	1,466	1,126	4,588	3,309
Ending balance	[1]	$ (84,729)	$ (45,114)	$ (84,729)	$ (45,114)

[1] All amounts are net of tax.