Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 6,387	$ 6,046	$ 33,241	$ 25,190
Other Comprehensive Income (Loss), net of tax:
Amortization of prior service cost, net of tax of $(5), $(8), $(11) and $(16), respectively	(14)	(12)	(28)	(23)
Net gain, net of tax of $41, $69, $80 and $145, respectively	108	101	217	194
Cash Flow Hedges, net of tax:
Unrealized gain (loss) on commodity contract cash flow hedges, net of tax of $429, $(554), $(327) and $(362), respectively	1,061	(875)	(728)	(537)
Total Other Comprehensive Income (Loss), net of tax	1,155	(786)	(539)	(366)
Comprehensive Income	$ 7,542	$ 5,260	$ 32,702	$ 24,824