Property, Plant and Mine Development – net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Property, equipment and mine development - net
Capital lease term			3 years
Monthly lease payment amount			$ 100
Purchase price option amount after end of lease term			100
Depletion, depreciation and amortization	$ 2,300	$ 1,100	$ 3,748	$ 1,895
Minimum
Property, equipment and mine development - net
Lease interest rate			4.50%
Maximum
Property, equipment and mine development - net
Lease interest rate			5.50%