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Commitments & Contingencies - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Long-term Purchase Commitment [Line Items]      
Operating lease expiration period 2025-12    
Rent expense $ 16,382,000 $ 13,516,000 $ 13,245,000
Minimum rental payments under capital leases 326,000    
Minimum rental payments under operating leases 54,268,000    
Minimal rental payments under operating leases, net of sublease payments 690,000    
Unconditional purchase obligations over next six years $ 72,459,000    
Minimum      
Long-term Purchase Commitment [Line Items]      
Operating lease term 1 year    
Unconditional purchase obligations 1 year    
Maximum      
Long-term Purchase Commitment [Line Items]      
Operating lease term 10 years    
Unconditional purchase obligations 5 years