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Commitments and Contingencies - Additional Information (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Commitments and Contingencies [Line Items]      
Rent expense $ 7.5 $ 7.7 $ 6.9
Purchase commitment, due in next twelve months 53.3    
Long-term purchase commitments $ 0.7    
Minimum      
Commitments and Contingencies [Line Items]      
Length of purchase commitments, in days 60 days    
Maximum      
Commitments and Contingencies [Line Items]      
Length of purchase commitments, in days 120 days