Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 71,498	$ 65,153	$ 56,580
Employee Benefits, net of tax:
Amortization of prior service cost, net of tax of $(18), $(20) and $(22), respectively	(59)	(57)	(55)
Net gain (loss), net of tax of $(41), $368, and $(49), respectively	(154)	1,052	(108)
Cash Flow Hedges, net of tax:
Unrealized gain (loss) on commodity contract cash flow hedges, net of tax of $1,392, $(176) and $(555), respectively	3,643	(434)	(1,371)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent	(28)
Total Other Comprehensive Income (Loss)	3,402	561	(1,534)
Comprehensive Income	$ 74,900	$ 65,714	$ 55,046