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Revenue from Contracts with Customers - Additional Information (Detail) - USD ($)
$ in Millions
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Revenue from Contract with Customer [Abstract]      
Remaining performance obligations $ 472.7    
Deferred contract costs 58.9 $ 83.3  
Amortization of deferred contract costs $ 240.6   $ 220.5