Other Income and Loss - Components of Other Income and Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Other Income And Loss [Abstract]
Interest income	$ 238	$ 137
Other income (loss)	(24)	110
Total	$ 214	$ 247

The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_NonoperatingIncomeExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration