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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]      
Accumulated impairment losses $ 0   $ 0
Amortization expense on intangible assets $ 5,400,000 $ 911,000