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Interest in Joint Operation - Additional Information (Detail) - Gruyere Gold project [member]
oz in Millions, $ in Millions, $ in Millions
 12 Months Ended
Dec. 13, 2016
Dec. 31, 2018
USD ($)
oz
Dec. 31, 2018
AUD ($)
oz
Dec. 31, 2017
AUD ($)
Dec. 31, 2016
AUD ($)
Disclosure of joint operations [line items]          
Percentage of ownership in joint operation: Gruyere Gold project 50.00%        
Proportion of ownership interest in joint venture with Gold Road Resources   50.00% 50.00%    
Acquisition date fair value of total consideration transferred     $ 350.0    
Percentage of royalty     1.50%    
Share of production after total mine production in ounces | oz   2 2    
Cash Consideration paid on effective date     $ 250.0    
Deferred Payment     100.0    
Transaction costs incurred   $ 13.3 18.5    
Cash consideration - deferred payment paid     $ 15.0 $ 78.0 $ 7.0