v2.4.1.9
Fair Value - Quantitative Information About Level Three Fair Value Measurements (Details) (Fuel price derivatives - diesel, USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Fair value $ 11,849us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Option Model | Minimum  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Future retail price of diesel (in usd per gallon) 3.72wex_FairValueInputsPricePerGallon
/ us-gaap_FinancialInstrumentAxis
= wex_FuelPriceDerivativesDieselMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ValuationTechniqueAxis
= wex_OptionModelMember
Option Model | Maximum  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Future retail price of diesel (in usd per gallon) 3.86wex_FairValueInputsPricePerGallon
/ us-gaap_FinancialInstrumentAxis
= wex_FuelPriceDerivativesDieselMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ValuationTechniqueAxis
= wex_OptionModelMember