Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Cash payments (net of refunds) for income taxes	$ 1.5		$ 8.9	$ 7.6	$ 21.8
Effective income tax rate	29.10%		28.40%	29.70%	39.70%
Income tax rate				21.00%		35.00%
Measurement period adjustment, decrease in income tax liability		$ 0.4
One-time transition tax on foreign subsidiaries' untaxed accumulated earnings, income tax benefit		$ 0.4