Other Comprehensive Income (Loss) (Changes in Accumulated Other Comprehensive Income (Loss) by Component (Net of Income Taxes)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	$ 3,000,196
Other comprehensive income before reclassifications	(22,342)	$ (15,663)	$ 29,284
Amounts reclassified from accumulated other comprehensive income (loss)	(3,498)	(1,551)	(631)
Other comprehensive (loss) income, Net of Tax Amount	(25,840)	(17,214)	28,653
Ending balance	2,927,924	3,000,196
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(29,819)	(12,605)	(41,258)
Other comprehensive (loss) income, Net of Tax Amount	(25,840)	(17,214)	28,653
Ending balance	(55,659)	(29,819)	(12,605)
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(12,504)	(12,824)	(13,099)
Other comprehensive income before reclassifications	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	287	320	275
Other comprehensive (loss) income, Net of Tax Amount	287	320	275
Ending balance	(12,217)	(12,504)	(12,824)
Net Unrealized Gains (Losses) on Investment Securities Available for Sale [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(18,222)	(713)	(28,936)
Other comprehensive income before reclassifications	(22,405)	(15,806)	29,041
Amounts reclassified from accumulated other comprehensive income (loss)	(3,697)	(1,703)	(818)
Other comprehensive (loss) income, Net of Tax Amount	(26,102)	(17,509)	28,223
Ending balance	(44,324)	(18,222)	(713)
Post-retirement Unfunded Health Benefit [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	907	932	777
Other comprehensive income before reclassifications	63	143	243
Amounts reclassified from accumulated other comprehensive income (loss)	(88)	(168)	(88)
Other comprehensive (loss) income, Net of Tax Amount	(25)	(25)	155
Ending balance	$ 882	$ 907	$ 932