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CAPITAL STOCK - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands |  |  |  |  |  |  | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 14, 2018 | Sep. 20, 2016 | Jun. 16, 2016 | May 27, 2016 | Mar. 14, 2016 | Jun. 18, 2015 | Dec. 31, 2015 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Partners' capital account, units, sold in public offering (in shares) |  | 8,337,500 |  |  |  |  |  |  |  |
Shares issued, price per share (in dollars per share) |  | $ 1.80 |  |  |  |  |  |  |  |
Partners' capital account, units, sold in public offering, warrants per unit (in shares) |  | 0.5 |  |  |  |  |  |  |  |
Common stock, shares, issued (in shares) |  |  |  |  |  |  |  | 74,366,824 | 66,205,153 | 46,519,132
Shares issued for consulting services (in shares) |  |  |  |  |  |  |  | 122,854 | 0 | 0
Value assigned of equity interest issued |  |  |  |  |  |  |  | $ 569 | $ 370 | $ 479
Share Purchase Warrants Denominated in United States Dollars |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Fair value of warrants |  |  |  |  |  |  |  | $ 6,283 |  |
March 14, 2019 Expiration Date | Share Purchase Warrants Denominated in United States Dollars |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Exercise price of warrants (in dollars per share) |  |  |  |  |  |  |  | $ 3.20 |  |
Fair value of warrants |  |  |  |  |  |  |  | $ 662 |  |
Number of warrants outstanding (in shares) |  |  |  |  |  |  |  | 2,328,925 |  |
Nichols Ranch, Hank and Doughstick Properties |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares issued for acquisition (in shares) | 1,100,000 |  |  |  |  |  |  |  |  |
Total purchase price | $ 3,740 |  |  |  |  |  |  |  |  |
Roca Honda |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares issued for acquisition (in shares) |  |  |  | 1,212,173 |  |  |  |  |  |
Percentage of voting interests acquired |  |  |  | 40.00% |  |  |  |  |  |
Value assigned of equity interest issued |  |  |  | $ 2,680 |  |  |  |  |  |
Alta Mesa I S R Project |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares issued for acquisition (in shares) |  |  | 4,551,284 |  |  |  |  |  |  |
Total purchase price |  |  | $ 12,668 |  |  |  |  |  |  |
Percentage of voting interests acquired |  |  | 100.00% |  |  |  |  |  |  |
Value assigned of equity interest issued |  |  | $ 11,380 |  |  |  |  |  |  |
Uranerz Energy Corporation |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Total purchase price |  |  |  |  |  | $ 106,340 |  |  |  |
Percentage of voting interests acquired |  |  |  |  |  | 100.00% |  |  |  |
Value assigned of equity interest issued |  |  |  |  |  | $ 106,340 |  |  |  |
Shares issued for consulting services (in shares) |  |  |  |  |  |  | 889,436 |  |  |
Value assigned of equity interest issued |  |  |  |  |  |  | $ 3,930 |  |  |
At The Market Sale Of Stock |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Sale of stock, number of shares issued (in shares) |  |  |  |  |  |  |  | 14,283,254 |  | 200,225
Sale of stock consideration received |  |  |  |  |  |  |  | $ 32,190 | $ 14,550 | $ 540
Public Offerings |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Sale of stock, number of shares issued (in shares) |  |  |  |  | 5,031,250 |  |  | 7,576,288 | 3,822,561 | 6,538,038
Sale of stock consideration received |  | $ 15,010 |  |  | $ 12,080 |  |  |  |  |
Equity issuance, per Share amount (in dollars per share) |  |  |  |  | $ 2.40 |  |  |  |  |
Units issued during period, underlying shares (in shares) |  |  |  |  | 5,031,250 |  |  |  |  |
Units issued during period, underlying warrants (in shares) |  |  |  |  | 2,515,625 |  |  |  |  |
Investment warrants, exercise price (in dollars per share) |  |  |  |  | $ 3.20 |  |  |  |  |
Warrants issued during period, value |  |  |  |  | $ 2,090 |  |  |  |  |
Number of warrants granted in period (in shares) |  |  |  |  | 2,515,625 |  |  |  |  |
Partners' capital account, units, sold in public offering, common shares per unit (in shares) |  | 1 |  |  |  |  |  |  |  |
Common stock, shares, issued (in shares) |  | 8,337,500 |  |  |  |  |  |  |  |
Number of warrants issued (in shares) |  | 4,168,750 |  |  |  |  |  |  |  |
Exercise price of warrants (in dollars per share) |  | $ 2.45 |  |  |  |  |  |  |  |
Fair value of warrants |  | $ 3,170 |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares issued for acquisition (in shares) |  |  |  |  |  | 24,457,773 |  |  |  |
Common Stock | Uranerz Energy Corporation |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Value assigned of equity interest issued |  |  |  |  |  | $ 101,744 |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Shares issued for consulting services (in shares) |  |  |  |  |  |  |  | 0 |  | 206,612
Value assigned of equity interest issued |  |  |  |  |  |  |  |  |  | $ 479
Common Stock | At The Market Sale Of Stock |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |
Shares Issued For Cash By At The Market Offering Shares |  |  |  |  |  |  |  |  | 7,202,479 |

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