Taxation - Tax holiday effect (Details) - CNY (¥) ¥ / shares in Units, ¥ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Taxation
Tax holiday effect	¥ (13,163)	¥ 622	¥ 1,385
Basic and diluted benefit per share effect		¥ 0.00	¥ 0.00
Basic and diluted benefit per share	¥ (0.04)

Per share amount effect of the income tax benefit resulting from the income tax holidays granted by taxing jurisdictions.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI http://asc.fasb.org/extlink&oid=116825942&loc=d3e330215-122817

Name:	us-gaap_IncomeTaxHolidayIncomeTaxBenefitsPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration