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Shareholders' equity - Summary of Calculation of Dividends and Interest on Capital (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Dividends [abstract]
Legal reserve, percentage	5.00%	5.00%	5.00%
Mandatory minimum dividend, percentage	25.00%	25.00%	25.00%

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- Definition

Disclosure of dividends.

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No definition available.

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- Definition

Legal reserve percentage.

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No definition available.

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- Definition

Mandatory minimum dividend percentage.

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No definition available.

+ Details

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