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Hedging Instruments - Additional Information (Details)
oz in Thousands, $ in Millions
3 Months Ended
Apr. 30, 2019
USD ($)
oz
Jul. 31, 2012
USD ($)
2012 4.40% Series B Notes, due July 2012    
Derivative [Line Items]    
Debt instrument face amount | $   $ 250.0
Interest Rate Swap | 2012 Debt Issuance    
Derivative [Line Items]    
Unrealized loss on interest rate swaps | $ $ 17.0  
Interest Rate Swap | 2014 Debt Issuance    
Derivative [Line Items]    
Unrealized loss on interest rate swaps | $ $ 3.5  
Foreign Exchange Forward | Maximum    
Derivative [Line Items]    
Term of contract (months) 12 months  
Precious Metal Forward Contracts | Maximum    
Derivative [Line Items]    
Term of contract (months) 18 months  
Platinum    
Derivative [Line Items]    
Precious metal derivatives, ounces outstanding (ounces) | oz 30  
Silver    
Derivative [Line Items]    
Precious metal derivatives, ounces outstanding (ounces) | oz 497  
Gold    
Derivative [Line Items]    
Precious metal derivatives, ounces outstanding (ounces) | oz 70