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Goodwill and Intangibles - Additional Information (Detail)
9 Months Ended
Sep. 30, 2018
USD ($)
Acquisition
Sep. 30, 2017
USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]    
Number of immaterial acquisitions | Acquisition 1  
Goodwill impairment $ 0 $ 0
Increase in gross carrying amount of intangibles $ 21,400,000