Income Taxes - Additional Information - Uncertain Tax Positions (Detail)	12 Months Ended
Dec. 31, 2017
Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Open tax year	2014
Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Open tax year	2016

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration