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, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	$ 2,927,924
Other comprehensive income (loss) before reclassifications	714	$ (22,342)	$ (15,663)
Amounts reclassified from accumulated other comprehensive income (loss)	191	(3,498)	(1,551)
Net current period other comprehensive income (loss)	905	(25,840)	(17,214)
Ending balance	2,961,566	2,927,924
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(55,659)	(29,819)	(12,605)
Ending balance	(54,754)	(55,659)	(29,819)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(12,217)	(12,504)	(12,824)
Other comprehensive income (loss) before reclassifications	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	80	287	320
Net current period other comprehensive income (loss)	80	287	320
Ending balance	(12,137)	(12,217)	(12,504)
Net Unrealized Gains (Losses) on Investment Securities Available for Sale
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	(44,324)	(18,222)	(713)
Other comprehensive income (loss) before reclassifications	676	(22,405)	(15,806)
Amounts reclassified from accumulated other comprehensive income (loss)	178	(3,697)	(1,703)
Net current period other comprehensive income (loss)	854	(26,102)	(17,509)
Ending balance	(43,470)	(44,324)	(18,222)
Post-Retirement Unfunded Health Benefit
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Beginning balance	882	907	932
Other comprehensive income (loss) before reclassifications	38	63	143
Amounts reclassified from accumulated other comprehensive income (loss)	(67)	(88)	(168)
Net current period other comprehensive income (loss)	(29)	(25)	(25)
Ending balance	$ 853	$ 882	$ 907

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

+ References

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-Publisher FASB
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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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