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STOCKHOLDERS' EQUITY (Common Stock, 2018 Purchase Agreement and LP Purchase Agreement) (Details) - USD ($) |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended | 36 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 20, 2020 | Apr. 08, 2020 | Mar. 26, 2020 | Jan. 14, 2020 | Aug. 09, 2019 | Feb. 01, 2019 | Sep. 14, 2018 | Sep. 07, 2018 | Apr. 30, 2020 | Mar. 25, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2020 | Apr. 06, 2020 | Jan. 29, 2019 | Jan. 01, 2019 | Dec. 20, 2018 | Dec. 19, 2018 | Sep. 06, 2018
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares authorized (in shares) |  |  |  |  |  |  |  |  |  |  | 150,000,000 | 150,000,000 |  | 150,000,000 |  |  | 250,000,000 | 150,000,000 | 150,000,000 |
Proceeds from exercise of warrants |  |  |  |  |  |  |  |  |  |  |  | $ 1,575,000 |  |  |  |  |  |  |  |
Conversion of convertible debt, plus interest, into common stock |  |  |  |  |  |  |  |  |  |  | $ 2,176,000 | $ 7,553,000 |  |  |  |  |  |  |  |
Shares issued (in shares) |  |  |  |  |  |  |  |  |  |  | 17,576,916 | 7,898,117 |  | 17,576,916 |  |  |  |  |  |
Common stock, shares outstanding (in shares) |  |  | 8,870,129 |  |  |  |  |  |  |  | 17,576,916 | 7,898,117 |  | 17,576,916 |  |  |  |  |  | 1,543,724
Issuance of common stock, net of issuance costs |  |  |  |  |  |  |  |  |  |  | $ 8,929,000 | $ 6,628,000 |  |  |  |  |  |  |  |
Conversion of debt into stock |  |  |  |  |  |  |  |  |  |  | $ 2,176,000 | $ 7,553,000 |  |  |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued in connection with the conversion of convertible notes |  |  |  |  |  |  |  |  |  |  | 3,980,145 | 2,511,173 |  |  |  |  |  |  |  |
Conversion of convertible notes into common stock (in shares) |  |  |  |  |  |  |  |  |  |  | 3,908,145 | 2,511,173 |  |  |  |  |  |  |  |
Number of shares converted from debt instrument (in shares) |  |  |  |  |  |  |  |  |  |  | 3,908,145 | 2,511,173 |  |  |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued for exercise of warrants |  |  |  |  |  |  |  |  |  |  |  | 310,200 |  |  |  |  |  |  |  |
Warrant exercises in period |  |  |  |  |  |  |  |  |  |  |  | 310,200 |  |  |  |  |  |  |  |
Proceeds from exercise of warrants |  |  |  |  |  |  |  |  |  |  |  | $ 1,600,000 |  |  |  |  |  |  |  |
Conversion of convertible debt, plus interest, into common stock |  |  |  |  |  |  |  |  |  |  | $ 2,200,000 | 7,600,000 |  |  |  |  |  |  |  |
Conversion of debt into stock |  |  |  |  |  |  |  |  |  |  | $ 2,200,000 | $ 7,600,000 |  |  |  |  |  |  |  |
Preferred Class B |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares converted (in shares) |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |  |  |  |  |  |
Leviston Resources LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of convertible debt, plus interest, into common stock |  |  |  |  |  |  |  |  |  |  |  | $ 700,000 |  |  |  |  |  |  |  |
Conversion of convertible notes into common stock (in shares) |  |  |  |  |  |  |  |  |  |  |  | 184,357 |  |  |  |  |  |  |  |
Number of shares converted from debt instrument (in shares) |  |  |  |  |  |  |  |  |  |  |  | 184,357 |  |  |  |  |  |  |  |
Conversion of debt into stock |  |  |  |  |  |  |  |  |  |  |  | $ 700,000 |  |  |  |  |  |  |  |
Leviston Resources LLC | Settled Litigation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of convertible notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 700,000 |  |  |  |
Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value of shares issued |  |  | $ 10,000,000 |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |
New shares issued (in shares) | 4,500,000 |  |  | 920,654 | 1,800,000 | 1,000,000 | 466,667 | 40,000 |  |  |  |  |  |  |  |  |  |  |  |
Shares issued (in shares) |  |  |  |  |  |  |  |  |  |  | 2,960,000 |  |  | 2,960,000 | 920,654 |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 7.05 |  |  |  |  |  |  |  |  |  |  |  |
Floor price (in dollars per share) |  |  |  |  |  |  |  | $ 0.10 |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering (in shares) |  |  | 4,980,000 |  |  |  |  |  |  |  | 1,040,654 | 2,778,077 | 328,590 |  |  |  |  |  |  |
Maximum percentage of shares issued |  |  |  |  |  |  |  | 19.99% |  |  |  |  |  |  |  |  |  |  |  |
Maximum number of shares issued |  |  |  |  |  |  |  | 308,590 |  |  |  |  |  |  |  |  |  |  |  |
Beneficial Ownership Cap |  |  |  |  |  |  |  | 4.99% |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, net of issuance costs |  |  |  |  |  |  |  |  |  |  | $ 1,400,000 |  | $ 1,400,000 | $ 9,400,000 |  |  |  |  |  |
Proceeds from sale of stock |  |  |  |  |  |  |  |  |  |  |  | $ 6,600,000 |  |  |  |  |  |  |  |
Lincoln Park [Member] | Subsequent Events |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering (in shares) |  |  |  |  |  |  |  |  |  | 500,000 |  |  |  |  |  |  |  |  |  |
Issuance of common stock, net of issuance costs |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |  |  |
Minimum | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  | $ 1.50 |  |  |  |  | $ 1.50 |  |  |  |  |  |  |  |  |  |  |  |
Maximum | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value of shares issued |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering (in shares) |  |  |  |  |  |  |  | 30,000 |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering based on market price |  |  |  |  |  |  |  | 36,666 |  |  |  |  |  |  |  |  |  |  |  |
LP 2020 Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, net of issuance costs |  |  |  |  |  |  |  |  |  |  | $ 8,800,000 |  |  |  |  |  |  |  |  |
LP 2020 Purchase Agreement [Member] | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value of shares issued |  |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
New shares issued (in shares) |  | 1,770,000 | 250,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  | $ 0.7306 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering (in shares) |  |  |  |  |  |  |  |  |  |  | 4,480,000 |  |  |  |  |  |  |  |  |
Maximum percentage of shares issued |  |  | 19.99% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum number of shares issued |  |  | 1,774,024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beneficial Ownership Cap |  |  |  |  |  |  |  |  | 4.99% |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock, net of issuance costs |  |  |  |  |  |  |  |  |  |  | $ 7,500,000 |  |  |  |  |  |  |  |  |
LP 2020 Purchase Agreement [Member] | Minimum | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  | $ 1.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
LP 2020 Purchase Agreement [Member] | Maximum | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value of shares issued |  |  | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering based on market price |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
LP 2020 Purchase Agreement [Member] | Closing Sale Price Above 1.00 [Member] | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering based on market price |  |  | 80,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
LP 2020 Purchase Agreement [Member] | Closing Sale Price Above 1.50 [Member] | Maximum | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold in offering based on market price |  |  | 100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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