Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 5,538	$ 6,833	$ 38,779	$ 32,023
Other Comprehensive Income (Loss), net of tax:
Amortization of prior service cost, net of tax of $(5), $(8), $(16) and $(23), respectively	(14)	(11)	(42)	(35)
Net gain, net of tax of $38, $69, $118 and $212, respectively	100	102	317	297
Cash Flow Hedges, net of tax:
Unrealized gain (loss) on commodity contract cash flow hedges, net of tax of $257, $(15), $(70) and $(376), respectively	644	(104)	(83)	(643)
Total Other Comprehensive Income (Loss), net of tax	730	(13)	192	(381)
Comprehensive Income	$ 6,268	$ 6,820	$ 38,971	$ 31,642