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Fair value measurement (Details 2) - CNY (¥)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Short-term investments      
Impairment charges ¥ 0 ¥ 0 ¥ 0
Wealth management products      
Short-term investments      
Gross unrealized gains ¥ 11,000 ¥ 54,813,000