Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 41,140	$ 36,092	$ 32,787
Employee Benefits, net of tax:
Amortization of prior service cost, net of tax of $(27), $(24) and $(24), respectively	(40)	(34)	(36)
Net gain (loss), net of tax of $73, $(1,997) and $1,673, respectively	103	(3,076)	2,565
Commodity Contract Cash Flow Hedges [Abstract]
Unrealized loss on commodity contract cash flow hedges, net of tax of $(150), $(22) and $0, respectively	(227)	(33)	0
Total Other Comprehensive Income (Loss)	(164)	(3,143)	2,529
Comprehensive Income	$ 40,976	$ 32,949	$ 35,316