Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Abstract]
Net operating loss	$ 18,956	$ 17,194
Interest limitation carryforward	1,801	441
Capital loss carryforward	555	10
Alternative minimum tax credit	524	1,049
Stock-based compensation	135	613
Other	1,294	985
Total long-term deferred tax assets	23,265	20,292
Coal properties	(27,884)	(46,733)
Net deferred tax liability	$ (4,619)	$ (26,441)