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PLANT AND EQUIPMENT AND MINERAL PROPERTIES - Schedule of Summary of Mineral Properties (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Property, Plant and Equipment [Line Items] |  |  |
Abandonment of mineral properties | $ 287 | $ 1,036 | $ 2,770
Mineral properties | 83,539 | 92,625 |
Uranerz ISR properties (a) |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Mineral properties | 25,974 | 35,060 |
Sheep Mountain |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Mineral properties | 34,183 | 34,183 |
Roca Honda |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Mineral properties | 22,095 | 22,095 |
Other |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Mineral properties | $ 1,287 | $ 1,287 |

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- Definition The adjustment to expense previously capitalized costs of drilling exploratory wells when proved reserves are not found or when the entity obtains information that raises substantial doubt about the economic or operational viability of the project. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 40 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6475089&loc=d3e66625-109467 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 35 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=66906256&loc=d3e66150-109466 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 40 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6475089&loc=d3e66584-109467 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 40 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6475089&loc=d3e66610-109467 + Details
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- Definition Mineral properties, net of adjustments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 25 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=96866604&loc=d3e64895-109465 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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