2.4.0.84090 - Disclosure - Derivative Financial Instruments (Details)truefalseIn Millions, unless otherwise specifiedfalse1false USDtruefalseD2011Q2_M0627_InterestRateSwap27June2011Memberhttp://www.sec.gov/CIK0000837173duration2011-06-26T00:00:002011-06-27T00:00:00falsefalseInterest rate swap - June 2011us-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwlt_InterestRateSwap27June2011Memberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$2false truefalseD2011Q2_M06_InterestRateSwap27June2011Memberhttp://www.sec.gov/CIK0000837173duration2011-06-01T00:00:002011-06-30T00:00:00falsefalseInterest rate swap - June 2011us-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwlt_InterestRateSwap27June2011Memberus-gaap_DerivativeInstrumentRiskAxisexplicitMember3false truefalseD2008Q4_M12_InterestRateSwap30December2008Memberhttp://www.sec.gov/CIK0000837173duration2008-12-01T00:00:002008-12-31T00:00:00falsefalseInterest rate swap - December 2008us-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwlt_InterestRateSwap30December2008Memberus-gaap_DerivativeInstrumentRiskAxisexplicitMember4false USDtruefalse$I2008Q4_M1230_InterestRateSwap30December2008Memberhttp://www.sec.gov/CIK0000837173instant2008-12-30T00:00:000001-01-01T00:00:00falsefalseInterest rate swap - December 2008us-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwlt_InterestRateSwap30December2008Memberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$5false USDtruefalseD2011Q2_M0627_InterestRateCapMemberhttp://www.sec.gov/CIK0000837173duration2011-06-26T00:00:002011-06-27T00:00:00falsefalseInterest rate capus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_InterestRateCapMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$6false truefalseD2011Q2_M06_InterestRateCapMemberhttp://www.sec.gov/CIK0000837173duration2011-06-01T00:00:002011-06-30T00:00:00falsefalseInterest rate capus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_InterestRateCapMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMember7false truefalseD2011Q2_M0627_CommodityContractMemberhttp://www.sec.gov/CIK0000837173duration2011-06-26T00:00:002011-06-27T00:00:00falsefalseNatural Gas Hedgeus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CommodityContractMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMember8false truefalse$I2011Q2_M0607_CommodityContractMemberhttp://www.sec.gov/CIK0000837173instant2011-06-07T00:00:000001-01-01T00:00:00falsefalseNatural Gas Hedgeus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CommodityContractMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0Millions_of_BTUStandardhttp://www.xbrl.org/2009/utrMMBTUutr0DollarPerMMBtuDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2009/utrMMBTUutr0USDUSD1true 3us-gaap_DerivativeLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse00falsefalsefalse8falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Fair Value of Financial Instruments2false 4us-gaap_NotionalAmountOfInterestRateCashFlowHedgeDerivativesus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse450000000450.0USD$falsetruefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4truefalsefalse3150000031.5USD$falsetruefalse5truefalsefalse255000000255.0USD$falsetruefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse00falsefalsefalse8falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryAggregate notional amount of all interest rate derivatives designated as hedging instruments in cash flow hedges. Notional amount refers to the monetary amount specified in the interest rate derivative contract.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Notional Amount -URI http://asc.fasb.org/extlink&oid=6519104 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959 false2Notional value3false 4us-gaap_DebtInstrumentDescriptionOfVariableRateBasisus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse003-month LIBORfalsefalsefalse3falsefalsefalse001-month LIBORfalsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalse6falsefalsefalse003-month LIBORfalsefalsefalse7falsefalsefalse00falsefalsefalse8falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringThe reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.No definition available.false0Debt instrument, description of variable rate basis4false 4us-gaap_DerivativeRemainingMaturity1us-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse003 yearsfalsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse003 yearsfalsefalsefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse001 yearfalsefalsefalse8falsefalsefalse00falsefalsefalsexbrli:durationItemTypenaPeriod remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.No definition available.false0Agreement period5false 4us-gaap_DerivativeFixedInterestRateus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.01170.0117falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4truetruefalse0.01840.0184falsefalsefalse5falsetruefalse00falsefalsefalse6falsetruefalse00falsefalsefalse7falsetruefalse00falsefalsefalse8falsetruefalse00falsefalsefalsenum:percentItemTypepureFixed interest rate related to the interest rate derivative.No definition available.false0Fixed rate (as a percent)6false 4wlt_DerivativeNumberOfMonthlyInterestPaymentsHedgedwlt_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse0062 monthsfalsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse00falsefalsefalse8falsefalsefalse00falsefalsefalsexbrli:durationItemTypenaNumber of monthly interest payments, which are protected against the variability in expected future cash flows attributable to changes in the benchmark interest rate.No definition available.false0Number of monthly interest payments, hedged7false 4wlt_DerivativeNumberOfMonthlyInterestPaymentswlt_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse0064 monthsfalsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse00falsefalsefalse8falsefalsefalse00falsefalsefalsexbrli:durationItemTypenaNumber of monthly interest payments required under an equipment financing arrangement.No definition available.false0Number of monthly interest payments8false 4us-gaap_DerivativeCapInterestRateus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsetruefalse00falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalse5truetruefalse0.02000.0200falsefalsefalse6falsetruefalse00falsefalsefalse7falsetruefalse00falsefalsefalse8falsetruefalse00falsefalsefalsenum:percentItemTypepureCap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.No definition available.false0Fixed rate (as a percent)9false 4invest_DerivativeNonmonetaryNotionalAmountinvest_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse00falsefalsefalse8truefalsefalse42000004200000falsefalsefalsexbrli:decimalItemTypedecimalAggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B false256Amount hedged (in mmbtus)10false 4us-gaap_DerivativeAverageForwardPriceus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalse6falsefalsefalse00falsefalsefalse7falsefalsefalse00falsefalsefalse8truefalsefalse5.005.00falsefalsefalseus-types:perUnitItemTypedecimalThe average forward price on the group of price risk forward or futures contracts, such as gas futures contracts.No definition available.false0Price per mmbtu of forecasted natural gas (in dollars per mmbtu)11false 4us-gaap_DerivativeNonmonetaryNotionalAmountPercentOfRequiredNeedCoverageus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsetruefalse00falsefalsefalse2falsetruefalse00falsefalsefalse3falsetruefalse00falsefalsefalse4falsetruefalse00falsefalsefalse5falsetruefalse00falsefalsefalse6falsetruefalse00falsefalsefalse7falsetruefalse00falsefalsefalse8truetruefalse0.300.30falsefalsefalsenum:percentItemTypepureThe percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.No definition available.false0Percentage of forecasted natural gas to be hedgedfalseDerivative Financial Instruments (Details) (USD $)HundredThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.walterenergy.com/role/DisclosureDerivativeFinancialInstrumentsDetails811