Other Income (Schedule of Other Income) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other income:
MSHA reimbursement	$ 180		$ 89	$ 833	$ 1,725
Other	529		314	968	901
Total other income	667		572	1,065	3,053
Savoy [Member]
Other income:
Equity income (loss)			153		409
Loss on disposal of equity method investment		$ (538)		(538)
Sunrise Energy [Member]
Other income:
Equity income (loss)	$ (42)		$ 16	$ (198)	$ 18