Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Comprehensive Income (Loss), Before Tax [Abstract]
Foreign currency translation adjustment	$ (35)	$ 270	$ (202)
Reclassification of net income (loss) on derivative instruments	614	614	613
Postretirement medical liability adjustment	(175)	346	1,257
Other comprehensive income (loss)	404	1,230	1,668
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	0	0	0
Reclassification of net income (loss) on derivative instruments	(162)	(116)	(242)
Postretirement medical liability adjustment	44	(133)	(484)
Other comprehensive income (loss)	(118)	(249)	(726)
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustment	(35)	270	(202)
Reclassification of net income (loss) on derivative instruments	452	498	371
Postretirement medical liability adjustment	(131)	213	773
Other comprehensive income (loss)	286	981	$ 942
Accumulated Other Comprehensive Income, Net of Tax [Abstract]
Foreign currency translation	1,413	1,448
Derivative instruments designated as cash flow hedges	(11,181)	(11,633)
Postretirement medical plans	120	251
Accumulated other comprehensive loss	$ (9,648)	$ (9,934)