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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
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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

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