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Subsequent Events - Summary of Allocation of Preliminary Purchase Price (Parenthetical) (Detail) |  | 3 Months Ended
--- | --- | ---
Apr. 11, 2018 USD ($) oz | Mar. 31, 2018
Business Acquisition [Line Items] |  |
Post-closing matters |  | ETF Securities has 45 business days following completion of the acquisition to provide a closing balance sheet.
Subsequent Event [Member] |  |
Business Acquisition [Line Items] |  |
Upfront consideration paid | $ | $ 0 |
Estimated target working capital | $ | $ 8,500,000 |
April 1, 2018 through March 31, 2058 [Member] | Subsequent Event [Member] |  |
Business Acquisition [Line Items] |  |
Fixed payments ounces of gold per year | oz | 9,500 |
April 1, 2058 and Thereafter [Member] | Subsequent Event [Member] |  |
Business Acquisition [Line Items] |  |
Fixed payments ounces of gold per year | oz | 6,333 |

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Estimated target working capital amount, as defined within the Share Sale Agreement. + References No definition available. + Details
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