Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Comprehensive Income (Loss), Before Tax [Abstract]
Foreign currency translation adjustment	$ 25	$ 558	$ 265
Reclassification of net gains on derivative instruments	(2,169)	(1,125)	(1,110)
Realized loss on cash flow hedging derivatives	0	0	(18,388)
Postretirement medical liability adjustment	317	504	134
Other comprehensive (loss) income	(1,827)	(63)	(19,099)
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	0	0	0
Reclassification of net gains on derivative instruments	831	427	426
Realized loss on cash flow hedging derivatives	0	0	7,243
Postretirement medical liability adjustment	(122)	(194)	(52)
Other comprehensive (loss) income	709	233	7,617
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustment	25	558	265
Reclassification of net gains on derivative instruments	(1,338)	(698)	(684)
Realized loss on cash flow hedging derivatives	0	0	(11,145)
Postretirement medical liability adjustment	195	310	82
Other comprehensive (loss) income	(1,118)	170	$ (11,482)
Accumulated Other Comprehensive Income, Net of Tax [Abstract]
Foreign currency translation	1,380	1,355
Derivative instruments designated as cash flow hedges	(10,352)	(9,014)
Pension and postretirement medical plans	(742)	(937)
Accumulated other comprehensive loss	$ (9,714)	$ (8,596)