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

ETF Securities has 45 business days following completion of the acquisition to provide a closing balance sheet.

$ 8,500,000

6,333