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Major Group Investments Direct and Indirect - Summary of Share Held in Investments in Associates Joint Ventures other Equity Investments and Percentage of Beneficial Interest (Parenthetical) (Detail) - shares
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2016
Cardinal Resources Limited Options [member] | Equity investments [member]    
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]    
Effective interest rate in stock option 20.00%  
Marverix Metals Incorporated [Member]    
Disclosure of Investments in Associates Joint Venture and Other Equity Investments [line items]    
Common shares 10,000,000 10,000,000
Percentage of ownership on diluted basis 20.50%