Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Income	$ 9,261	$ 5,621	$ 49,146	$ 42,589
Amortization of prior service cost, net of tax of $(5), $(5), $(15) and $(15), respectively	(14)	(14)	(42)	(43)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	(80)	(34)	(240)	(275)
Unrealized gain on commodity contract cash flow hedges, net of tax of $282, $152, $935 and $496, respectively	740	324	2,450	1,193
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent	27		(10)
Other comprehensive income (loss)	833	344	2,638	1,425
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	10,094	5,965	51,784	44,014
Net Income	9,261	5,621	49,146	42,589
Other Comprehensive Income (Loss), net of tax:
Amortization of prior service cost, net of tax of $(5), $(5), $(15) and $(15), respectively	(14)	(14)	(42)	(43)
Net gain, net of tax of $28, $10, $83 and $95, respectively	80	34	240	275
Cash Flow Hedges, net of tax:
Unrealized gain on commodity contract cash flow hedges, net of tax of $282, $152, $935 and $496, respectively	740	324	2,450	1,193
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent	27		(10)
Total Other Comprehensive Income, net of tax	833	344	2,638	1,425
Comprehensive Income	10,094	5,965	51,784	44,014
Retained Earnings [Member]
Net Income	9,261	5,621	49,146	42,589
Net Income	$ 9,261	$ 5,621	$ 49,146	$ 42,589