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Income Tax Provision - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Income Tax Disclosure [Abstract]          
Effective income tax rates (3.90%)   14.60% 0.20% 12.60%
Excess tax benefit $ 11.5   $ 8.5 $ 20.7 $ 18.6
Effective income tax rate excluding excess tax benefit 26.70%   37.30% 27.00% 37.70%
Change in tax rate, income tax benefit   $ 26.0      
Income tax payments       $ 7.1 $ 27.5