XML 425 R147.htm IDEA: XBRL DOCUMENT v3.19.1
Acquisition of Asanko Gold - Summary of Key Assumptions Used to Determine Fair Value of the Net Identifiable Assets Acquired (Detail) - $ / oz
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of detailed information about business combination [line items]    
Discount rate 10.27%  
Life-of-mine - 2019 to 2030 12 years  
Within one year [member] | US Dollars [member]    
Disclosure of detailed information about business combination [line items]    
US$ gold price 1,200  
Later than one year [member] | US Dollars [member]    
Disclosure of detailed information about business combination [line items]    
US$ gold price 1,300 1,300
Life-of-mine - 2019 to 2030 75 years 78 years