Financial instruments (Details 8) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Series H bonds [Member]
Financial instruments [Line Items]
Contract amount	$ 191,638
Currency	UF
Derivative contracts, Maturity	Jan. 05, 2018
Series O bonds [Member]
Financial instruments [Line Items]
Contract amount	$ 58,748
Currency	UF
Derivative contracts, Maturity	Feb. 01, 2022

The description of the currency of the primary economic environment in which the entity operates.

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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-IssueDate 2017-01-01
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-Subparagraph c
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