Significant accounting policies - Impairment of long-lived assets other than goodwill (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Impairment of long lived assets
Impairment loss	¥ 0	¥ 0	¥ 0
Impairment charge	¥ 5,080	¥ 42,529	¥ 0

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 350
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration