Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 56,580	$ 58,124	$ 44,675
Employee Benefits, net of tax:
Amortization of prior service cost, net of tax of $(22), $(31) and $(29), respectively	(55)	(46)	(48)
Net (loss)/gain, net of tax of $(49), $432, and $178, respectively	(108)	663	268
Cash Flow Hedges, net of tax:
Unrealized (loss)/gain on commodity contract cash flow hedges, net of tax of $(555), $(8) and $496, respectively	(1,371)	(11)	742
Total Other Comprehensive Income (Loss)	(1,534)	606	962
Comprehensive Income	$ 55,046	$ 58,730	$ 45,637