2.4.0.82411402 - Disclosure - Gas Reserves (details)truefalseIn Thousands, unless otherwise specifiedfalse1false USDfalsefalseD2013Q2YTDhttp://www.sec.gov/CIK0000073020duration2013-01-01T00:00:002013-06-30T00:00:00numberStandardhttp://www.xbrl.org/2003/instancepurexbrli0usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$2false USDfalsefalseD2012Q2YTDhttp://www.sec.gov/CIK0000073020duration2012-01-01T00:00:002012-06-30T00:00:00numberStandardhttp://www.xbrl.org/2003/instancepurexbrli0usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$3false USDfalsefalse$I2012Q4SDhttp://www.sec.gov/CIK0000073020instant2012-12-31T00:00:000001-01-01T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 1nwn_GasReservesAbstractnwn_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Gas Reserves [Abstract]2false 2nwn_GasReservesPercentGasSuppliesYtdnwn_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.060.06falsefalsefalse2truetruefalse0.030.03falsefalsefalse3falsetruefalse00falsefalsefalsenum:percentItemTypepurePercent of total gas supplies that were from gas reserves.No definition available.false0Gas Reserves Percent Gas Supplies YTD3false 2nwn_GasReservesCurrentnwn_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse1532400015324USD$falsetruefalse2truefalsefalse1102100011021USD$falsetruefalse3truefalsefalse1496600014966USD$falsetruefalsexbrli:monetaryItemTypemonetaryCarrying amount as of the balance sheet date of investments in Gas Reserves expected to be recovered within one year or the normal operating cycle if longer.No definition available.false2Gas Reserves, Current4false 2nwn_GasReservesNoncurrentGrossnwn_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse126215000126215falsefalsefalse2truefalsefalse6909700069097falsefalsefalse3truefalsefalse9217900092179falsefalsefalsexbrli:monetaryItemTypemonetaryGross carrying amount as of the balance sheet date of investments in Gas Reserves expected to be recovered in longer than one year.No definition available.false2Gas Reserves Noncurrent Gross5false 2nwn_GasReservesAmortizationnwn_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1245300012453falsefalsefalse2truefalsefalse40710004071falsefalsefalse3truefalsefalse74860007486falsefalsefalsexbrli:monetaryItemTypemonetaryCumulative regulatory amortization of gas reserves investment.No definition available.false2Gas Reserves Amortization6false 2nwn_TotalGasReservesnwn_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse129086000129086falsefalsefalse2truefalsefalse7604700076047falsefalsefalse3truefalsefalse9965900099659falsefalsefalsexbrli:monetaryItemTypemonetaryTotal gas reserves net of amortization.No definition available.false2Total Gas Reserves7false 2nwn_DeferredTaxesRelatedToGasReservesnwn_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse3996300039963falsefalsefalse2truefalsefalse2683900026839falsefalsefalse3truefalsefalse2832900028329falsefalsefalsexbrli:monetaryItemTypemonetaryDeferred taxes related to gas reservesNo definition available.false2Deferred Taxes Related To Gas Reserves8false 2nwn_NetGasReservesInvestmentnwn_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse8912300089123USD$falsetruefalse2truefalsefalse4920800049208USD$falsetruefalse3truefalsefalse7133000071330USD$falsetruefalsexbrli:monetaryItemTypemonetaryGas reserves investment net of amortization and deferred taxes.No definition available.false2Net Gas Reserves InvestmentfalseGas Reserves (details) (USD $)ThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.nwnatural.com/role/GasReservesDetails38