Income taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Components of Deferred Tax Assets [Line Items]
Non-capital losses carryforwards	$ 74,351	$ 59,956
Research and development deductions	15,812	16,349
Book amortization in excess of tax	(737)	(914)
Revenue recognized for tax purposes in excess of revenue recognized for accounting purposes	5,279	5,128
Tax value in excess of accounting value in lease inducements	627	705
Equity accounted for investment	3,375	3,038
Federal R&E credits	3,897
Deductible stock options	2,457	1,632
Other	1,218	1,111
Total deferred tax assets	114,795	102,762
Valuation allowance	(114,795)	(102,762)
Net deferred tax assets (liabilities)	0	0
Federal
Components of Deferred Tax Assets [Line Items]
Investment tax credits	5,872	7,325
Provincial
Components of Deferred Tax Assets [Line Items]
Investment tax credits	$ 2,644	$ 4,535