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Goodwill and Intangible Assets, Net - Additional Information (Detail) - USD ($)
12 Months Ended
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]        
Goodwill   $ 51,889,000 $ 51,889,000  
Goodwill impairment amount $ 0 0 0 $ 0
Amortization of intangible assets   $ 900,000 $ 1,600,000 $ 1,600,000