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Shareholders' equity - Outstanding (Detail)
Dec. 31, 2019
EquityInstruments
shares
Dec. 31, 2018
EquityInstruments
shares
Dec. 31, 2017
EquityInstruments
Shareholders' equity      
Common share outstanding | shares 189,381,388 186,692,481  
Stock options | EquityInstruments 836,427 1,015,409 955,603
Restricted Share Units | EquityInstruments 108,978 115,337  
Total | shares 190,326,793 187,823,227