2.4.0.82408402 - Disclosure - Debt (details)truefalseIn Thousands, unless otherwise specifiedfalse1false USDfalsefalseD2013Q2YTDhttp://www.sec.gov/CIK0000073020duration2013-01-01T00:00:002013-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$2false USDfalsefalse$I2012Q4SDhttp://www.sec.gov/CIK0000073020instant2012-12-31T00:00:000001-01-01T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false USDfalsefalse$I2012Q2http://www.sec.gov/CIK0000073020instant2012-06-30T00:00:000001-01-01T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 1us-gaap_LongtermDebtCurrentAndNoncurrentAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Long-term Debt, Current and Noncurrent [Abstract]2false 2us-gaap_DebtInstrumentDescriptionus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00At June 30, 2013, our gas storage segment’s long-term debt consisted of $40 million of senior secured debt with a maturity date of November 30, 2016. This debt consists of $20 million of fixed rate debt with an interest rate of 7.75% and $20 million of variable interest rate debt, which currently has an interest rate of 7.00%. The debt is secured by all of the membership interests in Gill Ranch and is nonrecourse to NW Natural. falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringIdentification of the lender and information about a contractual promise to repay a short-term or long-term obligation, which includes borrowings under lines of credit, notes payable, commercial paper, bonds payable, debentures, and other contractual obligations for payment. This may include rationale for entering into the arrangement, significant terms of the arrangement, which may include amount, repayment terms, priority, collateral required, debt covenants, borrowing capacity, call features, participation rights, conversion provisions, sinking-fund requirements, voting rights, basis for conversion if convertible and remarketing provisions. The description may be provided for individual debt instruments, rational groupings of debt instruments, or by debt in total.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 false0Debt Instrument, Description3false 2us-gaap_LongTermDebtMaturitiesRepaymentTermsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00At June 30, 2013, our utility's long-term debt consisted of $651.7 million of first mortgage bonds (FMBs) with maturity dates ranging from 2014 through 2042, interest rates ranging from 3.176% to 9.05%, and a weighted-average coupon rate of 5.71%. During the six months ended June 30, 2012, we did not issue or redeem any FMBs. falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringDisclosure of timing of required repayments, sinking fund requirements, and other redeemable securities at fixed or determinable prices and dates in the five years immediately following the date of the latest balance sheet presented in the financial statements, and the amount thereafter to fully repay the principal of long-term debt. These disclosures may be made either on an individual debt or security basis, by type of debt or security basis, or on a combined basis.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 false0Long-term Debt, Maturities, Repayment Terms4true 1us-gaap_LongTermDebtAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Long-term Debt, Unclassified [Abstract]5false 2us-gaap_MediumTermNotesus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse691700000691700USD$falsetruefalse2truefalsefalse691700000691700USD$falsetruefalse3truefalsefalse641700000641700USD$falsetruefalsexbrli:monetaryItemTypemonetaryIncluding the current and noncurrent portions, carrying value at the balance sheet date of a financial instrument used to receive debt funding on a regular basis with original maturities ranging from 5-10 years.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 false2Carrying Amount6false 2us-gaap_DebtInstrumentFairValueus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse769679000769679falsefalsefalse2truefalsefalse834664000834664falsefalsefalse3truefalsefalse768429000768429falsefalsefalsexbrli:monetaryItemTypemonetaryFair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13476-108611 false2Estimated Fair Value7true 1us-gaap_ShortTermBorrowingsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Short-term Debt [Abstract]8false 2nwn_CommercialPaperMaximumMaturitynwn_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse0057 daysfalsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringCommercial Paper, Maximum MaturityNo definition available.false0Commercial Paper, Maximum Maturity9false 2nwn_CommercialPaperAverageMaturitynwn_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse0043 daysfalsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringCommercial Paper, Average MaturityNo definition available.false0Commercial Paper, Average Maturity10false 2us-gaap_ShortTermBorrowingsus-gaap_truecreditinstantfalsefalsefalsefalsefalsefalsefalsefalse1truefalsefalse136000000136000USD$falsetruefalse2truefalsefalse190250000190250USD$falsetruefalse3truefalsefalse113200000113200USD$falsetruefalsexbrli:monetaryItemTypemonetaryReflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.Reference 1: 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