2.4.0.82412401 - Disclosure - Investments (details)truefalsefalse1false falsefalseI2013Q2http://www.sec.gov/CIK0000073020instant2013-06-30T00:00:000001-01-01T00:00:00numberStandardhttp://www.xbrl.org/2003/instancepurexbrli01true 1us-gaap_LongTermInvestmentsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Long-term Investments [Abstract]2false 2us-gaap_EquityMethodInvestmentOwnershipPercentageus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.50.5falsefalsefalsenum:percentItemTypepureThe percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 false0Equity Method Investment, Ownership PercentagefalseInvestments (details)UnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.nwnatural.com/role/InvestmentsDetails12