Income Taxes - Deferred Taxes in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Non-current assets	$ 164.5	$ 149.9
Other non-current liabilities	(1.6)	(1.2)
Net deferred tax assets	$ 162.9	$ 148.7

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards classified as noncurrent.

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Name:	us-gaap_DeferredTaxAssetsNetNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant