Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, Ngls and Natural Gas Reserves (Parenthetical) (Details)

v2.4.1.9
Supplemental Oil and Gas Disclosures - Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, Ngls and Natural Gas Reserves (Parenthetical) (Details)
 12 Months Ended
Dec. 31, 2014
MMBoe
Dec. 31, 2013
MMBoe
Dec. 31, 2012
MMBoe
Dec. 31, 2011
MMBoe
Reserve Quantities [Line Items]        
Proved undeveloped reserves, that will not be developed with in five years 1.4us-gaap_ProvedUndevelopedReserveBOE1      
Percentage of proved undeveloped reserves that will be developed with in five years 96.00%wti_PercentageOfProvedUndevelopedReservesExpectedToBeDeveloped      
Wells expected to be drilled, year 2020      
Barrel Equivalent        
Reserve Quantities [Line Items]        
Revisions of previous estimates 4.1us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1],[2] (3.8)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1],[3] (4.6)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1],[4]  
Extensions and discoveries 9.7us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1],[5] 20.2us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1],[6] 15.7us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1],[7]  
Proved reserves 120.0us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1] 117.7us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1] 117.5us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1] 116.9us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember 		[1]
Barrel Equivalent | Proved Undeveloped Reserves        
Reserve Quantities [Line Items]        
Proved reserves 36.7us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= wti_ProvedUndevelopedReservesMember 		[1],[8] 31.6us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= wti_ProvedUndevelopedReservesMember 		[1] 30.6us-gaap_ProvedDevelopedAndUndevelopedReserveNetEnergy
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= wti_BarrelEquivalentMember
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= wti_ProvedUndevelopedReservesMember 		[1]  
Changes due to price        
Reserve Quantities [Line Items]        
Revisions of previous estimates 0.3us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesDueToPriceMember 		1.9us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesDueToPriceMember 		1.3us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesDueToPriceMember 		 
Changes at the Spraberry field        
Reserve Quantities [Line Items]        
Revisions of previous estimates (3.9)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheSpraberryFieldMember 		(4.9)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheSpraberryFieldMember 		(3.0)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheSpraberryFieldMember 		 
Extensions and discoveries 4.1us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheSpraberryFieldMember 		12.6us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheSpraberryFieldMember 		11.6us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheSpraberryFieldMember 		 
Changes at the High Island 22 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   (2.3)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheHighIsland22FieldMember 		   
Extensions and discoveries     2.7us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheHighIsland22FieldMember 		 
Changes at the Ship Shoal 349/359 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   (1.3)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheShipShoal349359FieldMember 		   
Changes at the Main Pass 98 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   0.7us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheMainPass98FieldMember 		   
Changes at the South Timbalier 314 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   0.7us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtSouthTimbalierThreeOneFourFieldMember 		   
Changes at the Main Pass 108 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   0.6us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheMainPass108FieldMember 		   
Changes at the South Timbalier 176 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   0.5us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtSouthTimbalierOneSevenSixFieldMember 		   
Changes at the Ship Shoal 349 field        
Reserve Quantities [Line Items]        
Extensions and discoveries   4.2us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtShipShoalThreeFourNineMember 		   
Changes at the Mississippi Canyon 698 field        
Reserve Quantities [Line Items]        
Extensions and discoveries   1.9us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtMississippiCanyon698FieldMember 		   
Changes at the Fairway field        
Reserve Quantities [Line Items]        
Revisions of previous estimates 2.4us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheFairwayFieldMember 		     
Changes at the Mississippi Canyon 800 field        
Reserve Quantities [Line Items]        
Revisions of previous estimates 1.2us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheMississippiCanyonEightHundredFieldMember 		     
Various field positive revisions        
Reserve Quantities [Line Items]        
Revisions of previous estimates 6.4us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_VariousFieldPositiveRevisionsMember 		     
Various field negative revisions        
Reserve Quantities [Line Items]        
Revisions of previous estimates (2.4)us-gaap_ProvedDevelopedAndUndevelopedReserveRevisionOfPreviousEstimateEnergy
/ us-gaap_StatementGeographicalAxis
= wti_VariousFieldNegativeRevisionsMember 		     
Changes at the Mississippi Canyon 782 field        
Reserve Quantities [Line Items]        
Extensions and discoveries 4.1us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
/ us-gaap_StatementGeographicalAxis
= wti_ChangesAtTheMississippiCanyonSevenEightTwoFieldMember 		     
[1] The conversion to barrels of oil equivalent and cubic feet equivalent were determined using the energy-equivalent ratio of six Mcf of natural gas to one Bbl of crude oil, condensate or NGLs (totals may not compute due to rounding). The energy-equivalent ratio does not assume price equivalency, and the energy-equivalent prices for oil, NGLs and natural gas may differ significantly.
[2] Includes upwards revisions due to price of 0.3 MMBoe; positive revisions of 2.4 MMBoe at our Fairway field, 1.2 MMBoe at our Mississippi Canyon 800 field and 6.4 MMBoe at various fields; and negative revisions of 3.9 MMBoe at our Spraberry field and 2.4 MMBoe at various other fields.
[3] Includes upward revision due to price of 1.9 MMBoe; negative revisions of 4.9 MMBoe at our Spraberry field for performance and technical changes, 2.3 MMBoe at our High Island 21/22 field for performance, 1.3 MMBoe at our Ship Shoal 349/359 field for performance; and positive performance revisions of 0.7 MMBoe at our Main Pass 98 field, 0.7 MMBoe at our South Timbalier 314, 0.6 MMBoe at our Main Pass 108 field and 0.5 MMBoe our South Timbalier 176 field.
[4] Includes downward revisions due to price of 1.3 MMBoe and negative performance revisions of 3.0 MMBoe at our Spraberry field.
[5] Includes extensions and discoveries of 4.1 MMBoe at our Spraberry field and 4.1 MMBoe at our Mississippi Canyon 782 field.
[6] Includes extensions and discoveries of 12.6 MMBoe at our Spraberry field, 4.2 MMBoe at our Ship Shoal 349 field and 1.9 MMBoe at our Mississippi Canyon 698 field.
[7] Includes extensions and discoveries of 11.6 MMBoe at our Spraberry field and extensions and discoveries of 2.7 MMBoe at our High Island 21/22 field.
[8] We believe that we will be able to develop all but 1.4 MMBoe of the reserves classified as proved undeveloped (“PUDs”), or approximately 96%, out of the total of 36.7 MMBoe classified as PUDs at December 31, 2014, within five years from the date such reserves were initially recorded. The exception is at the Mississippi Canyon 243 field (Matterhorn) where the field is being developed using a single floating tension leg platform requiring an extended sequential development plan. The platform cannot support a rig that would allow additional wells to be drilled, but can support a rig to allow sidetracking of wells. These PUDs were originally recorded in our reserves as of December 31, 2010. The development of the 1.4 MMBoe of PUDs will be delayed until an existing well is depleted and available to sidetrack. Based on the latest reserve report, a well is expected to be drilled to develop the Mississippi Canyon 243 field (Matterhorn) PUDs in 2020.