Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Effective rate of tax	28.60%	18.30%
Statutory federal income tax rate	21.00%				35.00%
Decrease in the amount of excess tax benefits from stock-based compensation	$ 0.5
Undistributed earnings of foreign subsidiaries			$ 531.8		$ 531.8
US 2017 Tax Reform Act [Member]
Income Tax [Line Items]
Statutory federal income tax rate				21.00%
Additional income tax expense/benefit attributable to the enactment of the 2017 Tax Reform Act			32.7	$ (0.2)	32.7
US 2017 Tax Reform Act [Member] | One-Time Transition Tax on Mandatory Deemed Repatriation of Foreign Earnings [Member]
Income Tax [Line Items]
Additional income tax expense/benefit attributable to the enactment of the 2017 Tax Reform Act			32.7		32.7
US 2017 Tax Reform Act [Member] | Foreign Withholding Taxes on Certain Anticipated Distributions [Member]
Income Tax [Line Items]
Additional income tax expense/benefit attributable to the enactment of the 2017 Tax Reform Act			1.0		1.0
US 2017 Tax Reform Act [Member] | Remeasurement of Certain Deferred Tax Assets and Liabilities [Member]
Income Tax [Line Items]
Additional income tax expense/benefit attributable to the enactment of the 2017 Tax Reform Act			$ (1.0)		$ (1.0)