Lease liabilities - Additional Information (Detail)				3 Months Ended	9 Months Ended
	Sep. 26, 2019 USD ($) ft²	Dec. 22, 2016 ft²	Nov. 01, 2016 ft²	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Finance lease liability annual payment						$ 67,000
Lease rent for second year						$ 60,000
Present value of operating lease payments discount rate						6.00%
Deferred rent liability							$ 313,000
Operating lease costs				$ 300,000	$ 700,000
Finance lease discount rate						7.11%
Finance lease liability aggregate purchase price						$ 248,000
Accounting Standards Update 2016-02 [Member]
Lessee, Lease, Description [Line Items]
Finance lease liability annual payment						59,632
Finance lease liability aggregate purchase price						$ 298,160
Canada [Member]
Lessee, Lease, Description [Line Items]
Square feet of office space leased | ft²		2,500	10,946
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
USA [Member]
Lessee, Lease, Description [Line Items]
Square feet of office space leased | ft²	6,272
Lease agreement, commencement date	Oct. 01, 2019
Finance lease liability annual payment	$ 358,000
Lease rent for second year	$ 366,000
Lease agreement, expiration date	Sep. 30, 2021