Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provisional tax expense for the impact of remeasurement of deferred tax inventory		$ 84.3
US federal corporate tax rate	21.00%
Provisional transition tax liability net of foreign tax credits		36.6
Unrecognized tax benefits	$ 5.5	7.1
Accrued interest and penalties related to uncertain tax positions	$ 1.7	$ 2.7