Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net tax expense related to tax law change		$ 1.1
Reversal of liability for an uncertain tax position	$ 43.3

Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

Name:	us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration