Annual report pursuant to Section 13 and 15(d)

Income Taxes - Net Operating Loss and Tax Credit Carryovers (Details)

v2.4.1.9
Income Taxes - Net Operating Loss and Tax Credit Carryovers (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Internal Revenue Service (IRS)  
Operating Loss Carryforwards [Line Items]  
Net operating loss 516,393us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember
Internal Revenue Service (IRS) | Minimum  
Operating Loss Carryforwards [Line Items]  
Net operating loss, expiration year Dec. 31, 2032
Internal Revenue Service (IRS) | Maximum  
Operating Loss Carryforwards [Line Items]  
Net operating loss, expiration year Dec. 31, 2034
State and Local Jurisdiction  
Operating Loss Carryforwards [Line Items]  
Net operating loss 99,656us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember
State and Local Jurisdiction | Minimum  
Operating Loss Carryforwards [Line Items]  
Net operating loss, expiration year Dec. 31, 2021
State and Local Jurisdiction | Maximum  
Operating Loss Carryforwards [Line Items]  
Net operating loss, expiration year Dec. 31, 2029
Alternative Minimum Tax Credit  
Operating Loss Carryforwards [Line Items]  
Tax credit carryforward 12,091us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= wti_AlternativeMinimumTaxCreditMember
Tax credit carryforward, expiration year description Indefinite
General Business Tax Credit Carryforward  
Operating Loss Carryforwards [Line Items]  
Tax credit carryforward 406us-gaap_TaxCreditCarryforwardAmount
/ us-gaap_IncomeTaxAuthorityAxis
= wti_GeneralBusinessTaxCreditCarryforwardMember
General Business Tax Credit Carryforward | Minimum  
Operating Loss Carryforwards [Line Items]  
Tax credit carryforward, expiration year Dec. 31, 2027
General Business Tax Credit Carryforward | Maximum  
Operating Loss Carryforwards [Line Items]  
Tax credit carryforward, expiration year Dec. 31, 2028