Financial risk management (Details Text) (Detail) - BRL (R$) R$ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial Risk Management Details Text [Abstract]
Cash and cash equivalents	R$ 2,545,389	R$ 66,767	R$ 14,744	R$ 79,969	R$ 6,888	R$ 1,199

The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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