Federal Income Taxes - Schedule of Components of Future Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 80,491	$ 71,882
Mineral properties	13,970	11,375
Capital loss carryforwards	618
Restoration reserves	1,478	$ 1,360
Capitalized transaction costs	1,145
Other	946	$ 199
Deferred tax assets	98,648	84,816
Valuation allowance	(96,203)	(82,435)
Net deferred tax assets	2,445	2,381
Prepaids and other	68	100
Deferred tax liabilities current	68	100
Derivatives	(956)	(956)
Property, plant and equipment	(1,557)	(1,525)
Deferred tax liabilities noncurrent	(2,513)	(2,481)
Deferred tax liabilities	$ (2,445)	$ (2,381)
Net deferred tax asset (liability)