Note 3 - Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
PROPERTY, PLANT AND EQUIPMENT
Less: Accumulated depreciation and amortization	$ (30,100)	$ (15,809)
Total property, plant and equipment, net	171,945	149,205
Plant and Equipment
PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, gross	137,841	109,911
Construction in Progress
PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, gross	10,722	12,066
Mine Development
PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, gross	$ 53,482	$ 43,037