Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 28,664	$ 26,855
Other Comprehensive Income (Loss), net of tax:
Amortization of prior service cost, net of tax of $(5) and $(5), respectively	(14)	(14)
Net gain, net of tax of $42 and $41, respectively	121	108
Cash Flow Hedges, net of tax:
Unrealized gain (loss) on commodity contract cash flow hedges, net of tax of $1,194 and $(756), respectively	2,982	(1,788)
Total Other Comprehensive Income (Loss), net of tax	3,089	(1,694)
Comprehensive Income	$ 31,753	$ 25,161