Note 8 - Commitments and Contingencies (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Royalty Expense	$ 11,600	$ 1,800	$ 100
Operating Leases, Rent Expense, Net, Total	100	$ 400	$ 400
Mine Reclamation and Closing Liability, Noncurrent	12,700
Take-or-pay Purchase Commitments [Member]
Purchase Commitment, Remaining Minimum Amount Committed	900
Environmental Restoration Costs [Member]
Regulatory Liabilities, Total	$ 0