Other Long-Term Assets and Other Income (Schedule of Other Income) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other income:
MSHA reimbursements	[1]	$ 1,753
Coal storage fees			$ 600	$ 383
Miscellaneous		2,209	1,636	1,366
Other income		$ 3,962	$ 2,236	$ 1,749

[1] See “MSHA Reimbursements” in the MD&A section for a discussion of these amounts.