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Equity-Accounted Investees - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 06, 2017
Aug. 22, 2016
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Oct. 19, 2018
Dec. 31, 2010
Disclosure of equity-accounted investees [line items]              
Carrying value write down due to loss incurred by the entity     $ 233,300,000 $ 172,000,000      
Rusoro Mining Limited [member]              
Disclosure of equity-accounted investees [line items]              
Carrying value write down due to loss incurred by the entity             $ 0
Fair value of investment based on quoted market price     4,400,000 6,500,000      
Unrecognised share of profits     5,000,000 4,200,000      
Cumulative unrecognised share of losses     $ 207,800,000 202,800,000      
Pre and post award   $ 967,800,000          
Excess of pre and post award   $ 1,200,000,000          
Arbitration settlement $ 1,300,000,000            
Accrued interest percentage         9.00%    
Total settlement agreement amount           $ 1,280,000,000  
Maverix [member]              
Disclosure of equity-accounted investees [line items]              
Disposal of associates       33,800,000      
Derecognition Fair value of Investment       $ 19,200,000      
Lepanto Consolidated Mining Company [member]              
Disclosure of equity-accounted investees [line items]              
Interest on Joint Venture     60.00%