Net loss per share (Details) ¥ / shares in Units, $ / shares in Units, ¥ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2019 CNY (¥) ¥ / shares shares	Dec. 31, 2018 CNY (¥) ¥ / shares shares	Dec. 31, 2017 CNY (¥) ¥ / shares shares
Numerator:
Net loss	$ (15,000)	¥ (104,420)	¥ (416,694)	¥ (580,811)
Numerator for basic and diluted loss per share	$ (15,000)	¥ (104,420)	¥ (416,694)	¥ (580,811)
Denominator:
Weighted average ordinary shares outstanding-basic and diluted	308,364,918	308,364,918	304,542,400	301,610,060
Basic and diluted net loss per share attributable to ordinary shareholders \| (per share)	$ (0.05)	¥ (0.34)	¥ (1.37)	¥ (1.93)
Stock options and restricted share units
Net loss per share
Anti-dilutive and excluded from the calculation of diluted net loss per share (in shares)	27,421,502	27,421,502	26,635,519	27,407,348
Preferred shares
Net loss per share
Anti-dilutive and excluded from the calculation of diluted net loss per share (in shares)	0	0
ADS
Denominator:
Basic and diluted net loss per share attributable to ordinary shareholders \| (per share)	$ (0.73)	¥ (5.08)	¥ (20.55)	¥ (28.95)

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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