Accumulated Other Comprehensive Income (Loss) (Change in AOCI Components net of tax) (Details 2) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	$ 1,286,832	$ 1,268,200
Total Other Comprehensive Income (Loss)	41,933	7,165
Balance at End of Period	1,327,929	1,269,690
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(38,756)	(36,010)
Other Comprehensive Income (Loss) Before Reclassifications	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	374	246
Total Other Comprehensive Income (Loss)	374	246
Balance at End of Period	(38,382)	(35,764)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(31,112)	(51,043)
Other Comprehensive Income (Loss) Before Reclassifications	41,567	6,581
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	366	584
Total Other Comprehensive Income (Loss)	41,933	7,165
Balance at End of Period	10,821	(43,878)
Available-for-sale Securities \| Unrealized Gains and Losses on Net Investment Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	8,359	(10,447)
Other Comprehensive Income (Loss) Before Reclassifications	41,567	6,581
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(56)	47
Total Other Comprehensive Income (Loss)	41,511	6,628
Balance at End of Period	49,870	(3,819)
Held-to-maturity Securities \| Unrealized Gains and Losses on Net Investment Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(715)	(4,586)
Other Comprehensive Income (Loss) Before Reclassifications	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	48	291
Total Other Comprehensive Income (Loss)	48	291
Balance at End of Period	$ (667)	$ (4,295)

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.

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

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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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