Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation and Cash-Based Incentive Compensation - Schedule of Restricted Stock Units Outstanding (Details)

v2.4.1.9
Share-Based Compensation and Cash-Based Incentive Compensation - Schedule of Restricted Stock Units Outstanding (Details) (Restricted Stock Units (RSUs))
Mar. 31, 2015
Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Awards expected to vest by period 1,927,794us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,977,335us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
2015 | Restricted Stock Units subject to service requirements
    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Awards expected to vest by period 739,620us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= wti_RestrictedStockUnitsSubjectToServiceRequirementsMember
/ us-gaap_VestingAxis
= wti_TwoThousandFifteenMember 		 
2015 | Restricted Stock Units subject to service and other requirements
    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Awards expected to vest by period 87,701us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= wti_RestrictedStockUnitsSubjectToMarketPerformanceMetricsAndServiceRequirementsMember
/ us-gaap_VestingAxis
= wti_TwoThousandFifteenMember 		[1]  
2016 | Restricted Stock Units subject to service requirements
    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Awards expected to vest by period 1,100,473us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= wti_RestrictedStockUnitsSubjectToServiceRequirementsMember
/ us-gaap_VestingAxis
= wti_TwoThousandSixteenMember 		 
[1] In addition to service requirements, these RSUs are also subject to TSR performance requirements not yet measureable, with awards ranging from 0% to 200% of amounts granted.