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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Goodwill [Line Items]      
Goodwill, relates to acquisition $ 3,500,000 $ 3,500,000  
Impairment losses 0    
Amortization expense 2,900,000 $ 2,500,000 $ 1,900,000
Network Solutions [Member]      
Goodwill [Line Items]      
Goodwill, relates to acquisition 3,100,000    
Services & Support [Member]      
Goodwill [Line Items]      
Goodwill, relates to acquisition $ 400,000