Annual report pursuant to Section 13 and 15(d)

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

v2.4.1.9
Share-Based and Cash-Based Incentive Compensation - Schedule of Restricted Stock Units Outstanding (Details) (Restricted Stock Units (RSUs))
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Awards expected to vest by period 1,977,335us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,331,753us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 969,820us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,732,703us-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 759,234us-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 90,105us-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 1,127,996us-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.