INCOME TAXES - Deferred Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Components of deferred tax asset
Expected federal income tax rate (as a percent)	21.00%
Significant Components of Deferred Tax Assets
Operating loss carry forward		$ 62,480
Mineral properties		857
Share based compensation		823
Embedded derivatives		168
Other		15
Total deferred tax assets		64,343
Valuation allowance	$ (31,267)	(35,429)
Net deferred tax asset		28,914
Taxable temporary difference — Investment in EMLLC		(28,654)
Senior convertible notes debt discount		(260)
Deferred tax assets	31,367
Total deferred tax liabilities	148,890	28,914
Net operating loss carry-forwards		280,000
Operating loss carry forward subject to expiration		261,000
Operating loss carry forward not subject to expiration		19,000
Unrecognized tax benefits	$ 0	$ 0