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Share-based compensation - Schedule of fair value assumptions of share options granted (Details) - Stock options
12 Months Ended
Dec. 31, 2019
Year
$ / shares
Dec. 31, 2018
Year
$ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Expected dividend yield 0.00% 0.00%
Expected life | Year 5 5
Annualized volatility 100.00% 100.00%
Bottom of range    
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Grant date share price $ 6.45 $ 10.05
Exercise price $ 7.17 $ 10.05
Risk free interest rate 1.24% 1.97%
Top of range    
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Grant date share price $ 75.38 $ 142.71
Exercise price $ 75.38 $ 148.74
Risk free interest rate 1.90% 2.41%