Income Tax Expense - Summary of Tax Years Subject to Examination in Taxing Jurisdictions (Detail)	9 Months Ended
Sep. 30, 2018
United States [Member]
Income Tax Examination [Line Items]
Income tax year under examination	2015 and forward
Foreign [Member]
Income Tax Examination [Line Items]
Income tax year under examination	2011 and forward

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_IncomeTaxExaminationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration