Stockholders' Equity Accumulated Other comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	$ (4,272)	$ (6,713)	$ (4,272)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(3,732)	1,289
Amounts reclassified from accumulated other comprehensive income/(loss)	2,198	(728)
Net current-period other comprehensive income/(loss)	(1,534)	561
Accumulated other comprehensive loss at end of period		(6,267)	(6,713)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect	(907)
AOCI Changes For Defined Benefit Pension And Postretirement Plans [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	(4,743)	(5,928)	(4,743)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(602)	(872)
Amounts reclassified from accumulated other comprehensive income/(loss)	439	1,867
Net current-period other comprehensive income/(loss)	(163)	995
Accumulated other comprehensive loss at end of period		(4,933)	(5,928)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect	(1,022)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	471	(785)	471
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(3,130)	2,161
Amounts reclassified from accumulated other comprehensive income/(loss)	1,759	(2,595)
Net current-period other comprehensive income/(loss)	(1,371)	(434)
Accumulated other comprehensive loss at end of period		(1,334)	$ (785)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect	$ 115	$ (115)

Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]

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Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect

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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.

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

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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