Income Tax Provision - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Effective income tax rates	14.60%	17.20%	12.40%	25.20%
Federal income tax rate	35.00%	35.00%	35.00%	35.00%
Exess tax benefit	$ 8.5	$ 6.3	$ 18.6	$ 7.5
Effective income tax rate excluding excess tax benefit	37.50%	37.90%	37.90%	38.10%
Income tax payments			$ 27.5	$ 17.6