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Commitments and Contingencies - Total Rent Expense under Operating Lease (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Operating Leased Assets [Line Items]      
Rent expense under operating leases $ 15,123 $ 11,580 $ 9,362
Cost of Sales [Member]      
Operating Leased Assets [Line Items]      
Rent expense under operating leases 813 848 855
Administrative [Member]      
Operating Leased Assets [Line Items]      
Rent expense under operating leases $ 14,310 $ 10,732 $ 8,507