Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Stock-based compensation	$ 458	$ 347
Investment	827	1,227
Oil and gas properties	(15,711)	(2,234)
Net operating loss	7,583
Alternative minimum tax credit	4,388	4,043
Other	18
Net long-term deferred tax assets	(2,437)	3,383
Coal properties	(46,596)	(44,964)
Net deferred tax liability	$ 49,033	$ 41,581