2.2.0.7 false Cost and Fair Value Basis of Long Term Debt 01400 - Disclosure - Cost and Fair Value Basis of Long Term Debt true false false false 1 USD false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 EPS Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 $ 2 Disclosure - Cost and Fair Value Basis of Long-Term Debt 0 nwn_DisclosureCostAndFairValueBasisOfLongTermDebt nwn false na duration No definition available. false false false false false true false false false false false false 1 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 3 Cost and Fair Value Basis of Long-Term Debt 1 us-gaap_LongTermDebtTextBlock us-gaap true na duration No definition available. false false false false false false false false false false false false 1 false false false false 0 0 5.       Cost and Fair Value Basis of Long-Term Debt Cost of Long-Term Debt Our long-term debt consists of medium-term notes (MTNs) that have maturity dates from 2010 through 2035, and have interest rates ranging from 3.95 percent to 9.05 percent with a weighted-average coupon rate of 6.19 percent (see Note 5 in our 2009 Form 10-K). For the nine months ended September 30, 2010 we did not issue or redeem any MTNs. In March 2009, we issued $75 million of 5.37 percent secured MTNs due February 1, 2020, and in July 2009, we issued another $50 million of secured MTNs with an interest rate of 3.95 percent and a maturity of July 15, 2014.  Proceeds from these MTNs were used to fund utility capital expenditures, to redeem utility short-term and long-term debt, and to provide utility working capital for general corporate purposes. Fair Value of Long-Term Debt The following table provides an estimate of the fair value of our long-term debt including current maturities of long-term debt, using market prices in effect on the valuation date.  Because our debt outstanding does not trade in active markets, we used interest rates for outstanding debt issues that actively trade and have similar credit ratings, terms and remaining maturities to estimate fair value for our long-term debt issues.<div><table style="border-collapse:collapse;margin-top:20px;"><tr style="height: 20px"><td style="width: 390px; text-align:left;border-color:#000000;min-width:390px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td colspan="4" style="width: 200px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:200px;">September 30,</td><td style="width: 10px; text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 90px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:90px;">December 31,</td></tr><tr style="height: 20px"><td style="width: 390px; text-align:left;border-color:#000000;min-width:390px;">Thousands</td><td style="width: 10px; text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 90px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:90px;">2010</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 90px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:90px;">2009</td><td style="width: 10px; text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 90px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:90px;">2009</td></tr><tr style="height: 20px"><td style="width: 390px; text-align:left;border-color:#000000;min-width:390px;">Carrying amount</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:10px;">$</td><td style="width: 90px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 636,700</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:10px;">$</td><td style="width: 90px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 637,000</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:10px;">$</td><td style="width: 90px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 636,700</td></tr><tr style="height: 20px"><td style="width: 390px; text-align:left;border-color:#000000;min-width:390px;">Estimated fair value</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:right;border-color:#000000;min-width:10px;">$</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> 740,731</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:right;border-color:#000000;min-width:10px;">$</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> 670,116</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:right;border-color:#000000;min-width:10px;">$</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> 707,755</td></tr></table></div> 5.       Cost and Fair Value Basis of Long-Term Debt Cost of Long-Term Debt Our long-term debt consists of false false false us-types:textBlockItemType textblock This element may be used as a single block of text to encapsulate the entire disclosure for long-term borrowings including data and tables. 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