Annual report pursuant to Section 13 and 15(d)

Acquisitions and Divestitures - Additional Information (Details)

v2.4.1.9
Acquisitions and Divestitures - Additional Information (Details) (USD $)
 3 Months Ended 12 Months Ended 7 Months Ended 0 Months Ended 3 Months Ended 0 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Jul. 11, 2013
Sep. 26, 2013
Dec. 31, 2012
May 15, 2012
Sep. 15, 2014
Sep. 14, 2014
May 20, 2014
Oct. 17, 2013
Oct. 05, 2012
Block
acre
Business Acquisition [Line Items]                                          
Goodwill, acquired during period                 $ 0us-gaap_GoodwillAcquiredDuringPeriod $ 0us-gaap_GoodwillAcquiredDuringPeriod $ 0us-gaap_GoodwillAcquiredDuringPeriod                    
Revenues 196,677,000us-gaap_Revenues 234,521,000us-gaap_Revenues 262,994,000us-gaap_Revenues 254,516,000us-gaap_Revenues 244,928,000us-gaap_Revenues [1],[2] 244,555,000us-gaap_Revenues [1],[2] 235,383,000us-gaap_Revenues [1],[2] 259,222,000us-gaap_Revenues [1],[2] 948,708,000us-gaap_Revenues 984,088,000us-gaap_Revenues 874,491,000us-gaap_Revenues                    
DD&A                 511,102,000us-gaap_DepreciationAmortizationAndAccretionNet 451,529,000us-gaap_DepreciationAmortizationAndAccretionNet 356,232,000us-gaap_DepreciationAmortizationAndAccretionNet                    
Income tax expense                 (4,459,000)us-gaap_IncomeTaxExpenseBenefit 28,774,000us-gaap_IncomeTaxExpenseBenefit 47,547,000us-gaap_IncomeTaxExpenseBenefit                    
Net income (33,371,000)us-gaap_NetIncomeLoss 684,000us-gaap_NetIncomeLoss 9,837,000us-gaap_NetIncomeLoss 11,189,000us-gaap_NetIncomeLoss (11,886,000)us-gaap_NetIncomeLoss [1],[2] 14,194,000us-gaap_NetIncomeLoss [1],[2] 22,396,000us-gaap_NetIncomeLoss [1],[2] 26,618,000us-gaap_NetIncomeLoss [1],[2] (11,661,000)us-gaap_NetIncomeLoss 51,322,000us-gaap_NetIncomeLoss 71,984,000us-gaap_NetIncomeLoss                    
Fairway                                          
Business Acquisition [Line Items]                                          
Percentage of working interest                                 100.00%wti_PercentageOfWorkingInterest
/ us-gaap_BusinessAcquisitionAxis
= wti_FairwayPropertiesMember 		64.30%wti_PercentageOfWorkingInterest
/ us-gaap_BusinessAcquisitionAxis
= wti_FairwayPropertiesMember 		     
Goodwill, acquired during period                 0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_BusinessAcquisitionAxis
= wti_FairwayPropertiesMember 		                       
Woodside Properties                                          
Business Acquisition [Line Items]                                          
Percentage of working interest                                     20.00%wti_PercentageOfWorkingInterest
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		   
Goodwill, acquired during period                 0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		                       
Revenues                       28,400,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		                 
Lease operating expenses                       5,500,000us-gaap_OperatingCostsAndExpenses
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		                 
DD&A                       11,000,000us-gaap_DepreciationAmortizationAndAccretionNet
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		                 
Income tax expense                       4,200,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		                 
Net income                       7,700,000us-gaap_NetIncomeLoss
/ us-gaap_BusinessAcquisitionAxis
= wti_WoodsidePropertiesMember 		                 
Callon Properties                                          
Business Acquisition [Line Items]                                          
Percentage of working interest                                       15.00%wti_PercentageOfWorkingInterest
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		 
Goodwill, acquired during period                   0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                     
Revenues         5,800,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		      32,500,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                       
Lease operating expenses         1,300,000us-gaap_OperatingCostsAndExpenses
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		      6,600,000us-gaap_OperatingCostsAndExpenses
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                       
DD&A         2,400,000us-gaap_DepreciationAmortizationAndAccretionNet
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		      16,400,000us-gaap_DepreciationAmortizationAndAccretionNet
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                       
Income tax expense         700,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		      3,300,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                       
Net income         1,400,000us-gaap_NetIncomeLoss
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		      6,200,000us-gaap_NetIncomeLoss
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                       
Adjustments to purchase price                 600,000us-gaap_PaymentsForPreviousAcquisition
/ us-gaap_BusinessAcquisitionAxis
= wti_CallonPropertiesMember 		                       
Green Canyon Fields                                          
Business Acquisition [Line Items]                                          
Reversal of asset retirement obligation                         15,600,000us-gaap_AssetRetirementObligationLiabilitiesSettled
/ us-gaap_BusinessAcquisitionAxis
= wti_GreenCanyonFieldsMember 		               
Proceeds from sale of properties                         4,300,000us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
/ us-gaap_BusinessAcquisitionAxis
= wti_GreenCanyonFieldsMember 		               
West Delta Area Block Twenty Nine                                          
Business Acquisition [Line Items]                                          
Reversal of asset retirement obligation                           3,900,000us-gaap_AssetRetirementObligationLiabilitiesSettled
/ us-gaap_BusinessAcquisitionAxis
= wti_WestDeltaAreaBlockTwentyNineMember 		             
Proceeds from sale of properties                           14,700,000us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
/ us-gaap_BusinessAcquisitionAxis
= wti_WestDeltaAreaBlockTwentyNineMember 		             
West Delta Area Block Twenty Nine | Post Effective Date Repayment                                          
Business Acquisition [Line Items]                                          
Proceeds from sale of properties 1,700,000us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
/ us-gaap_BusinessAcquisitionAxis
= wti_WestDeltaAreaBlockTwentyNineMember
/ us-gaap_StatementScenarioAxis
= wti_PostEffectiveDateRepaymentMember 		              1,700,000us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
/ us-gaap_BusinessAcquisitionAxis
= wti_WestDeltaAreaBlockTwentyNineMember
/ us-gaap_StatementScenarioAxis
= wti_PostEffectiveDateRepaymentMember 		    1,700,000us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
/ us-gaap_BusinessAcquisitionAxis
= wti_WestDeltaAreaBlockTwentyNineMember
/ us-gaap_StatementScenarioAxis
= wti_PostEffectiveDateRepaymentMember 		                 
Newfield Properties                                          
Business Acquisition [Line Items]                                          
Goodwill, acquired during period                     0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		                   
Revenues                 121,100,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		127,100,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		        29,600,000us-gaap_Revenues
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		           
Lease operating expenses                 23,500,000us-gaap_OperatingCostsAndExpenses
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		26,700,000us-gaap_OperatingCostsAndExpenses
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		        5,400,000us-gaap_OperatingCostsAndExpenses
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		           
DD&A                 60,500,000us-gaap_DepreciationAmortizationAndAccretionNet
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		57,600,000us-gaap_DepreciationAmortizationAndAccretionNet
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		        11,900,000us-gaap_DepreciationAmortizationAndAccretionNet
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		           
Income tax expense                 13,000,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		15,000,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		        4,300,000us-gaap_IncomeTaxExpenseBenefit
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		           
Net income                 24,100,000us-gaap_NetIncomeLoss
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		27,800,000us-gaap_NetIncomeLoss
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		        8,000,000us-gaap_NetIncomeLoss
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		           
Adjustments to purchase price                   200,000us-gaap_PaymentsForPreviousAcquisition
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember 		                     
Number of federal offshore blocks                                         78wti_NumberOfFederalOffshoreBlocks
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember
Leasehold interest acres acquired, gross                                         416,000wti_NumberOfAcresOfOilAndGasLeaseholdInterestsAcquiredGross
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember
Leasehold interest acres acquired, net                                         268,000wti_NumberOfAcresOfOilAndGasLeaseholdInterestsAcquiredNet
/ us-gaap_BusinessAcquisitionAxis
= wti_NewfieldPropertiesMember
South Timbalier 41                                          
Business Acquisition [Line Items]                                          
Reversal of asset retirement obligation                               4,000,000us-gaap_AssetRetirementObligationLiabilitiesSettled
/ us-gaap_BusinessAcquisitionAxis
= wti_SouthTimbalierFortyOneMember 		         
Proceeds from sale of properties                               $ 30,500,000us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
/ us-gaap_BusinessAcquisitionAxis
= wti_SouthTimbalierFortyOneMember 		         
Percentage of non-operating working interest sold                               40.00%wti_NonOperatingWorkingInterestPercentageSold
/ us-gaap_BusinessAcquisitionAxis
= wti_SouthTimbalierFortyOneMember 		         
[1] The sum of the individual quarterly earnings per share may not agree with year-to-date earnings per share because each quarterly calculation is based on the income for that quarter and the weighted average number of shares outstanding during that quarter.
[2] In January 2014, we identified that we had been receiving an erroneous million British thermal unit (“MMBtu”) conversion factor from a third party that had the effect of understating natural gas production at our Viosca Knoll 783 field (Tahoe).  The incorrect conversion factor had been used on all natural gas production from the field since we acquired it in 2011.  The use of the incorrect conversion factor did not affect revenues, operating cash flows or royalty payments to the federal government but did impact reported natural gas production and the calculation of depletion expense.  We performed an analysis of the information, assessing both quantitative and qualitative factors, and determined that the impact on our net income reported for prior annual periods, as well as the impact to our earnings trend, was not material to 2011 and 2012 results, thus the adjustment was recognized in the fourth quarter of 2013.