Employee Benefit Plans Schedule of Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in AOCL [Roll Forward]
Accumulated other comprehensive loss (Beginning Bal)			$ (137,578)
Net actuarial loss	$ 653	$ 0	(5,291)	$ 0
Amortization of prior service credit	(46)	(46)	(91)	(91)
Amortization of actuarial loss	1,703	1,983	6,817	3,211
Settlement cost	0	361	0	1,726
Accumulated other comprehensive loss (Ending Bal)	(127,553)		(127,553)
Pension Plan [Member]
Changes in AOCL [Roll Forward]
Accumulated other comprehensive loss (Beginning Bal)	(98,261)	(56,236)	(97,226)	(58,584)
Net actuarial loss	386	0	(5,558)	0
Amortization of prior service credit	(46)	(46)	(91)	(91)
Amortization of actuarial loss	1,569	1,783	6,523	2,811
Settlement cost	0	361	0	1,726
Accumulated other comprehensive loss (Ending Bal)	(96,352)	(54,138)	(96,352)	(54,138)
Other Postretirement Benefits Plan [Member]
Changes in AOCL [Roll Forward]
Accumulated other comprehensive loss (Beginning Bal)	(6,437)	(7,681)	(6,597)	(7,881)
Net actuarial loss	267	0	267	0
Amortization of prior service credit	0	0	0	0
Amortization of actuarial loss	134	200	294	400
Settlement cost	0	0	0	0
Accumulated other comprehensive loss (Ending Bal)	$ (6,036)	$ (7,481)	$ (6,036)	$ (7,481)

Changes in AOCL [Roll Forward]

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

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Amount, after tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

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-Publisher FASB
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- Definition

Amount, after tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

+ References

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Amount, after tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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