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Goodwill and Intangibles - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]      
Goodwill impairment $ 0 $ 0 $ 0
Intangible asset impairment 0 0 0
Increase in gross carrying amount of intangibles 77,700,000 30,400,000  
Amortization expense on intangible assets 26,857,000 11,259,000 $ 6,264,000
Intangibles on business combination $ 76,800,000 $ 30,300,000