Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Percentage of Revenue by Major Customers (Parenthetical) (Details)

v2.4.1.9
Significant Accounting Policies - Percentage of Revenue by Major Customers (Parenthetical) (Details) (ConocoPhillips)
 12 Months Ended
Dec. 31, 2012
Entity
Companies Separated Into Two
  
Entity Wide Revenue Major Customer [Line Items]  
Number of companies separated 2wti_NumberOfCompaniesSeparated
/ us-gaap_InvestmentTypeAxis
= wti_HoldingsMember
/ us-gaap_MajorCustomersAxis
= wti_ConocoPhillipsMember
Sales Revenue Net | Customer Concentration Risk
  
Entity Wide Revenue Major Customer [Line Items]  
Percentage of receipts 16.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= wti_ConocoPhillipsMember 		[1]
Sales Revenue Net | Companies Separated Into Two | Customer Concentration Risk
  
Entity Wide Revenue Major Customer [Line Items]  
Percentage of receipts 8.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_InvestmentTypeAxis
= wti_HoldingsMember
/ us-gaap_MajorCustomersAxis
= wti_ConocoPhillipsMember
[1] (1) ConocoPhillips split into two separate companies during 2012 and individually were approximately 8% each.