Fixed assets - Schedule of net gains and losses on sales of fixed assets (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fixed assets:
Gains	$ 59	$ 259	$ 0
Losses	(49)	(128)	(71)
Total net gains (losses)	$ 10	$ 131	$ (71)

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

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