Income Taxes - Classification of Net Deferred Income Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Long-term deferred income tax assets	$ 563.8	$ 528.8
Long-term deferred income tax liabilities	(86.6)	(83.3)
Net deferred income tax asset	$ 477.2	$ 445.5