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Intangible Assets - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]      
Goodwill $ 0.6   $ 0.6
Amortization expense $ 7.6 $ 5.8