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Credit Facilities and Long-term Debt - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of detailed information about borrowings [line items]      
Uncommitted bank overdraft facilities $ 73,500,000 $ 70,000,000  
Amounts outstanding under overdraft facilities 0 0  
Credit Facility      
Disclosure of detailed information about borrowings [line items]      
Borrowings 187,500,000 227,500,000  
Commitment fees paid 1,300,000 1,400,000 $ 1,300,000
Letters of credit outstanding 23,200,000 25,800,000  
Term Loan      
Disclosure of detailed information about borrowings [line items]      
Face amount of debt instrument 250,000,000.0    
Borrowings 187,500,000 212,500,000  
Quarterly principal repayment $ 6,250,000    
Term Loan | London Interbank Offered Rate LIBOR | Bottom of range      
Disclosure of detailed information about borrowings [line items]      
Margin for borrowings 2.00%    
Term Loan | London Interbank Offered Rate LIBOR | Top of range      
Disclosure of detailed information about borrowings [line items]      
Margin for borrowings 3.00%    
Revolving Facility      
Disclosure of detailed information about borrowings [line items]      
Line of credit, maximum borrowing capacity $ 300,000,000    
Borrowings 0 $ 15,000,000  
Amount of accordion feature 150,000,000.0    
Uncommitted bank overdraft facilities $ 276,800,000    
Revolving Facility | Bottom of range      
Disclosure of detailed information about borrowings [line items]      
Margin for borrowings 0.60%    
Revolving Facility | Top of range      
Disclosure of detailed information about borrowings [line items]      
Margin for borrowings 1.40%    
Revolving Facility | London Interbank Offered Rate LIBOR | Bottom of range      
Disclosure of detailed information about borrowings [line items]      
Margin for borrowings 1.60%    
Revolving Facility | London Interbank Offered Rate LIBOR | Top of range      
Disclosure of detailed information about borrowings [line items]      
Margin for borrowings 2.40%    
Bridge Loan | Revolving Facility      
Disclosure of detailed information about borrowings [line items]      
Line of credit, maximum borrowing capacity $ 25,000,000.0    
Bridge Loan | Revolving Facility | Top of range      
Disclosure of detailed information about borrowings [line items]      
Debt instrument term 7 days