For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, more than one year after the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.26(c))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77902458&loc=d3e39927-112707

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

Commitments and Contingencies - Additional Information (Detail) $ in Thousands			12 Months Ended
	Dec. 22, 2016 ft²	Nov. 01, 2016 ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Contingencies And Commitments [Line Items]
Deferred rent liability			$ 313	$ 453
Operating lease costs			$ 700	$ 700	$ 400
Canada [Member]
Contingencies And Commitments [Line Items]
Lease agreement, commencement date	Dec. 22, 2016	Nov. 01, 2016
Lease agreement, expiration date	Jun. 30, 2019	Oct. 31, 2021
Lease agreement extended period		Oct. 31, 2026
Square feet of office space leased \| ft²	2,500	10,946