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Derivative Commodity Instruments (Impact Of Derivative Instruments Not Designated As Fair Value Hedges) (Details) (Commodity forward contracts [Member], Derivatives Not Designated As Hedging Instrument [Member], Cost of Sales [Member], USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (Loss) Recognized in Income on Derivative $ (9,244)us-gaap_DerivativeGainLossOnDerivativeNet    
Predecessor [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (Loss) Recognized in Income on Derivative   $ 5,438us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= wlkp_CommodityForwardContractsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember		 $ (11,961)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= wlkp_CommodityForwardContractsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember