Other Income (Schedule of Other Income) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other income:
MSHA reimbursement	$ 150		$ 1,250	$ 653	$ 1,636
Other	244		206	439	587
Other income	321		1,483	398	2,481
Savoy [Member]
Other income:
Equity income (loss)			44		256
Loss on disposal of equity method investment		$ (538)		(538)
Sunrise Energy [Member]
Other income:
Equity income (loss)	$ (73)		$ (17)	$ (156)	$ 2