Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt - Additional Information (Details)

v2.4.1.9
Long-Term Debt - Additional Information (Details) (USD $)
3 Months Ended 0 Months Ended
Mar. 31, 2015
Apr. 23, 2015
Dec. 31, 2014
Mar. 31, 2014
Apr. 30, 2015
Debt Instrument [Line Items]          
Senior notes interest rate 8.50%us-gaap_DebtInstrumentInterestRateStatedPercentage        
8.50% Senior Notes          
Debt Instrument [Line Items]          
Senior notes interest rate 8.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= wti_EightPointFivePercentSeniorNotesMember
  8.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= wti_EightPointFivePercentSeniorNotesMember
   
Senior notes payment terms semi-annually in arrears on June 15 and December 15        
Effective interest rate 8.40%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= wti_EightPointFivePercentSeniorNotesMember
    8.40%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= wti_EightPointFivePercentSeniorNotesMember
 
Senior notes maturity date Jun. 15, 2019        
Revolving Bank Credit Facility Due November 2018          
Debt Instrument [Line Items]          
Effective interest rate 3.20%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
       
Credit agreement expiration date Nov. 08, 2018        
Letters of credit outstanding 600,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
  600,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
   
Revolving bank credit facility maximum lender commitment 750,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
       
Line of credit, borrowing availability 235,400,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
       
Revolving Bank Credit Facility Due November 2018 | Subsequent Event          
Debt Instrument [Line Items]          
Credit agreement expiration date   Nov. 08, 2018      
Revolving bank credit facility borrowing base   $ 600,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
    $ 600,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= wti_RevolvingBankCreditFacilityDueNovemberTwoThousandEighteenMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember