Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Cost Incurred in Oil and Gas Property Acquisition Exploration and Development Activities (Parenthetical) (Details)

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Supplemental Oil and Gas Disclosures - Cost Incurred in Oil and Gas Property Acquisition Exploration and Development Activities (Parenthetical) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Capitalized Costs Oil And Gas Producing Activities Net [Abstract]      
Additions (reductions) of asset retirement obligations $ 88.0wti_AssetRetirementObligationPeriodIncreaseDecreaseDueToAcquisitionsIncurredAndRevisions $ 50.6wti_AssetRetirementObligationPeriodIncreaseDecreaseDueToAcquisitionsIncurredAndRevisions $ 86.9wti_AssetRetirementObligationPeriodIncreaseDecreaseDueToAcquisitionsIncurredAndRevisions
Seismic costs 9.0wti_SeismicCosts 8.9wti_SeismicCosts 6.2wti_SeismicCosts
Geological and geophysical costs $ 7.3wti_GeologicalAndGeophysicalCosts $ 5.9wti_GeologicalAndGeophysicalCosts $ 6.2wti_GeologicalAndGeophysicalCosts