Segment information (Details 3)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Customer D
Customers accounting for more than 5% of the Group's revenue	0	0	5
Customer C
Customers accounting for more than 5% of the Group's revenue	0	6	10
Customer B
Customers accounting for more than 5% of the Group's revenue	0	8	0
Customer A
Customers accounting for more than 5% of the Group's revenue	15	9	19

Description of risks that arise due to the volume of business transacted with a particular customer. At a minimum, the description informs financial statement users of the general nature of the risk, but excludes "Information about Major Customers" that may be disclosed elsewhere (for instance, segment disclosures).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI https://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 16
-URI https://asc.fasb.org/extlink&oid=99393423&loc=d3e6327-108592

Name:	us-gaap_ConcentrationRiskCustomer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration