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Share-based payments - Fair Value of Equity Component (Details) - Class B share-based payments
12 Months Ended
Dec. 31, 2019
$ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]  
Expected term, in years 1.0
Expected volatility 39.30%
Risk free interest rate 2.60%
Dividend yield 7.70%
FV at grant date per option $ 5,612
Discount for Lack of Marketability 8.40%