Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments - Cash Payments on Derivative Settlements, Net Included within Net Cash Provided by Operating Activities (Details)

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Derivative Financial Instruments - Cash Payments on Derivative Settlements, Net Included within Net Cash Provided by Operating Activities (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]      
Cash payments on derivative settlements, net $ 5,318wti_CashPaymentsReceiptsOnDerivativeSettlements $ 8,589wti_CashPaymentsReceiptsOnDerivativeSettlements $ 7,664wti_CashPaymentsReceiptsOnDerivativeSettlements