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Impairment fair value (Details 5) - Exploration and production [Member] | 3 Months Ended
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Mar. 31, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |
Fair value impairment | $ (1,400,000)
Fair value impairment after tax | $ (900,000)

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