Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 874	$ 777
Additions based on tax positions related to the current year	0	70
Balance at end of period	$ 874	$ 847

Amount of unrecognized tax benefits.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 10B
-URI http://asc.fasb.org/extlink&oid=84176650&loc=SL37586934-109318

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

Name:	us-gaap_UnrecognizedTaxBenefits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant