Stockholders' Equity Accumulated Other comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	$ (6,267)	$ (6,713)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	4,838	1,289
Amounts reclassified from accumulated other comprehensive income/(loss)	(1,436)	(728)
Net current-period other comprehensive income/(loss)	3,402	561
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect		(115)
Accumulated other comprehensive loss at end of period	(2,865)	(6,267)
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	(4,933)	(5,928)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(578)	(872)
Amounts reclassified from accumulated other comprehensive income/(loss)	365	1,867
Net current-period other comprehensive income/(loss)	(213)	995
Accumulated other comprehensive loss at end of period	(5,146)	(4,933)
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	(1,334)	(785)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	5,400	2,161
Amounts reclassified from accumulated other comprehensive income/(loss)	(1,757)	(2,595)
Net current-period other comprehensive income/(loss)	3,643	(434)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect		(115)
Accumulated other comprehensive loss at end of period	2,309	$ (1,334)
Accumulated (Gain) Loss from Interest Rate Swap Cash Flows Hedges
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	16
Amounts reclassified from accumulated other comprehensive income/(loss)	(44)
Net current-period other comprehensive income/(loss)	(28)
Accumulated other comprehensive loss at end of period	$ (28)