Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
PROPERTY, PLANT AND EQUIPMENT
Less: Accumulated depreciation and amortization	$ (24,690)	$ (15,809)
Total property, plant and equipment, net	164,193	149,205
Plant and Equipment, at Cost
PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, gross	130,218	109,911
Construction in Progress
PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, gross	10,252	12,066
Mine Development
PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, gross	$ 48,413	$ 43,037