PLANT AND EQUIPMENT AND MINERAL PROPERTIES - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Cost	$ 56,310	$ 56,310
Accumulated Depreciation	(28,117)	(26,467)
Net Book Value	28,193	29,843
Nichols Ranch
Property, Plant and Equipment [Line Items]
Cost	29,210	29,210
Accumulated Depreciation	(13,046)	(12,021)
Net Book Value	16,164	17,189
Alta Mesa
Property, Plant and Equipment [Line Items]
Cost	13,656	13,656
Accumulated Depreciation	(2,784)	(2,319)
Net Book Value	10,872	11,337
Equipment and other
Property, Plant and Equipment [Line Items]
Cost	13,444	13,444
Accumulated Depreciation	(12,287)	(12,127)
Net Book Value	$ 1,157	$ 1,317