Annual report pursuant to Section 13 and 15(d)

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

v2.4.1.9
Share-Based and Cash-Based Incentive Compensation - Schedule of Restricted Stock Units Outstanding (Parenthetical) (Details) (Restricted Stock Units (RSUs), 2015, Restricted Stock Units subject to service and other requirements)
 12 Months Ended
Dec. 31, 2014
Restricted Stock Units (RSUs) | 2015 | Restricted Stock Units subject to service and other requirements
  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Restricted stock units adjustments, percentage 0.00%wti_NumberOfRestrictedStockUnitsTargetAwardVestedRangeMinimum
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= wti_RestrictedStockUnitsSubjectToMarketPerformanceMetricsAndServiceRequirementsMember
/ us-gaap_VestingAxis
= wti_TwoThousandFifteenMember
Restricted stock units adjustments, percentage 200.00%wti_NumberOfRestrictedStockUnitsTargetAwardVestedRangeMaximum
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= wti_RestrictedStockUnitsSubjectToMarketPerformanceMetricsAndServiceRequirementsMember
/ us-gaap_VestingAxis
= wti_TwoThousandFifteenMember