Income Taxes - Additional Information (Detail)	9 Months Ended
Sep. 30, 2018 USD ($)
Income Tax Contingency [Line Items]
Adjustments to provisional amounts due to Tax Act	$ 0
Tax cuts and jobs act of 2017, accounting complete	false
Internal Revenue Service [Member]
Income Tax Contingency [Line Items]
Open tax year	2011 2012 2013 2014

Tax year that remains open to examination under enacted tax laws, in CCYY format.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

Name:	us-gaap_OpenTaxYear
Namespace Prefix:	us-gaap_
Data Type:	us-types:gYearListItemType
Balance Type:	na
Period Type:	duration