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Acquisition Of Asanko Gold - Summary of Acquisition Date Fair Value of Major Class of Consideration Transferred (Detail)
$ in Millions
Dec. 31, 2018
USD ($)
Disclosure of detailed information about business combination [line items]  
Cash - Asanko redeemable preference shares and equity $ 216.8
Total consideration transferred 165.0
Asanko [member]  
Disclosure of detailed information about business combination [line items]  
Cash - Asanko redeemable preference shares and equity $ 165.0