Other long-term obligations - Other liabilities and obligations (Details) - CAD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Deferred gain on sale-leaseback [Roll Forward]
Balance, beginning of year	$ 6,593	$ 8,438
Amortization of deferred gain on sale-leaseback	(1,845)	(1,845)
Balance, end of year	$ 4,748	$ 6,593

Amount of gain (loss) on sale and leaseback transaction from transfer of asset accounted for as sale.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 40
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121606570&loc=SL77919786-209982

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980

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