Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 44,675	$ 41,140	$ 36,092
Employee Benefits, net of tax:
Amortization of prior service cost, net of tax of ($29), $(27) and $(24), respectively	(48)	(40)	(34)
Net gain (loss), net of tax of $178, $73, and $(1,997), respectively	268	103	(3,076)
Cash Flow Hedges, net of tax:
Unrealized gain (loss) on commodity contract cash flow hedges, net of tax of $496, $(150) and $(22), respectively	742	(227)	(33)
Total Other Comprehensive Income (Loss)	962	(164)	(3,143)
Comprehensive Income	$ 45,637	$ 40,976	$ 32,949