Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 26,855	$ 19,144
Other Comprehensive (Loss) Income, net of tax:
Amortization of prior service cost, net of tax of $(5) and $(8), respectively	(14)	(11)
Net gain, net of tax of $41 and $77, respectively	108	93
Cash Flow Hedges, net of tax:
Unrealized (loss)/gain on commodity contract cash flow hedges, net of tax of ($756) and $192, respectively	(1,788)	338
Total Other Comprehensive (Loss) Income, net of tax	(1,694)	420
Comprehensive Income	$ 25,161	$ 19,564