v3.8.0.1
Valuation and Qualifying Accounts (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Allowance for doubtful accounts      
Balance December 31, 2016 $ 12.4 $ 7.8 $ 4.3
Provision for doubtful accounts 5.3 9.5 7.8
Write-off and adjustments (7.0) (5.6) (4.5)
Recoveries 0.7 0.7 0.2
Balance December 31, 2017 $ 11.4 $ 12.4 $ 7.8