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Segment information (Details 3)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Customer A
Customers accounting for more than 5% of the Group's revenue	9%	19%	15%
Customer B
Customers accounting for more than 5% of the Group's revenue	8%	0%	0%
Customer C
Customers accounting for more than 5% of the Group's revenue	6%	10%	0%
Customer D
Customers accounting for more than 5% of the Group's revenue	0%	5%	0%
Customer E
Customers accounting for more than 5% of the Group's revenue	0%	0%	7%

X

- Definition

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).

+ References

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

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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6327-108592

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