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DEFERRED REVENUE - Changes in Deferred Revenue (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Revenue From Contract With Customer [Roll Forward]      
Accretion expense - gold prepayment1 $ 9.9 $ 9.3  
Revenue from contracts with customers 189.7 $ 179.8 $ 170.5
Current portion of deferred revenue 189.7    
Non-current deferred revenue 0.0    
Receivables from contracts with customers $ 189.7