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Property and Equipment - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property, Plant and Equipment [Abstract]      
Non- cash charges to write-off certain property and equipment, primarily computer software development costs $ 418,000 $ 0 $ 535,000
Depreciation and amortization expense $ 25,787,000 $ 27,493,000 $ 26,649,000