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Stockholders' equity - Summary of Cost of Shares Purchased and Average Cost of Treasury Shares and Market Price (Detail) - R$ / shares
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Ordinary shares [member]    
Disclosure of classes of share capital [line items]    
Market price per share R$ 32.03 R$ 30.05
Preference shares [member]    
Disclosure of classes of share capital [line items]    
Average cost 21.76 21.76
Market price per share R$ 37.10 35.50
Preference shares [member] | Bottom of range [member]    
Disclosure of classes of share capital [line items]    
Cost per share   37.45
Preference shares [member] | Weighted average [member]    
Disclosure of classes of share capital [line items]    
Cost per share   38.95
Preference shares [member] | Top of range [member]    
Disclosure of classes of share capital [line items]    
Cost per share   R$ 40.06