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Commitments and Contingencies - Additional Information (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Long Term Purchase Commitment [Line Items]    
Unconditional purchase obligations, term 6 years  
Unconditional purchase obligations $ 72,714  
Bank of America, N.A.    
Long Term Purchase Commitment [Line Items]    
Amount outstanding under letters of credit $ 857 $ 933
Minimum    
Long Term Purchase Commitment [Line Items]    
Unconditional purchase obligations, term 1 year  
Maximum    
Long Term Purchase Commitment [Line Items]    
Unconditional purchase obligations, term 6 years