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MINERAL PROPERTY INTERESTS, PLANT AND EQUIPMENT AND CONSTRUCTION IN PROGRESS (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018
Property, Plant and Equipment [Line Items] |  |
Subtotal | $ 476,443 | $ 459,006
Less: accumulated depreciation | (40,784) | (35,127)
Net carrying value | 435,659 | 423,879
Mineral property interests |  |
Property, Plant and Equipment [Line Items] |  |
Subtotal | 336,372 | 326,086
Land |  |
Property, Plant and Equipment [Line Items] |  |
Subtotal | 8,708 | 8,699
Construction in process |  |
Property, Plant and Equipment [Line Items] |  |
Subtotal | 2,508 | 74,643
Plant and equipment |  |
Property, Plant and Equipment [Line Items] |  |
Subtotal | 128,855 | 49,578
Gold Bar mine | Construction in process |  |
Interest expense |  |
Interest Expense, Debt | $ 1,400 | $ 800

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