Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in the components of accumulated other comprehensive loss, net of taxes
Balance	$ 2,736,941	$ 2,675,040	$ 2,651,111
Other comprehensive income (loss)	(36,752)	198	(5,692)
Balance	2,476,485	2,736,941	2,675,040
Components of accumulated other comprehensive loss, net of taxes, resulting from other-than-temporarily impaired securities
Non-credit other-than-temporary impairment losses on securities available for sale	0	0
Accumulated Other Comprehensive Loss
Changes in the components of accumulated other comprehensive loss, net of taxes
Balance	(51,259)	(51,457)	(45,765)
Other comprehensive income (loss)	(36,752)	198	(5,692)
Balance	(88,011)	(51,259)	(51,457)
Pension and other benefits
Changes in the components of accumulated other comprehensive loss, net of taxes
Balance	(26,883)	(35,869)	(19,221)
Other comprehensive income (loss)	(3,354)	8,986	(16,648)
Balance	(30,237)	(26,883)	(35,869)
Investment securities
Changes in the components of accumulated other comprehensive loss, net of taxes
Balance	(25,106)	(15,533)	(27,339)
Other comprehensive income (loss)	(34,852)	(9,573)	11,806
Balance	(59,958)	(25,106)	(15,533)
Cash flow derivative hedges
Changes in the components of accumulated other comprehensive loss, net of taxes
Balance	730	(55)	795
Other comprehensive income (loss)	1,454	785	(850)
Balance	$ 2,184	$ 730	$ (55)

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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- Definition

Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

+ References

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- Definition

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

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- Definition

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.

+ References

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