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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]          
Accumulated impairment losses $ 0   $ 0   $ 0
Amortization expense on intangible assets $ 4,900,000 $ 8,700,000 $ 10,300,000 $ 9,700,000