2.2.0.7 false Income Tax 01600 - Disclosure - Income Tax 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 Income Tax 0 nwn_DisclosureIncomeTax 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 Income Tax 1 us-gaap_IncomeTaxDisclosureTextBlock 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 7.        Income Tax The effective income tax rate for the nine months ended September 30, 2010 and 2009 varied from the combined federal and state statutory tax rates principally due to the following:<div><table style="border-collapse:collapse;margin-top:20px;"><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;"> </td><td colspan="4" style="width: 220px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:220px;">September 30,</td><td style="width: 20px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:20px;"> </td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;"> </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: 20px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:20px;"> </td><td style="width: 20px; border-top-style:solid;border-top-width:1px;text-align:center;border-color:#000000;min-width:20px;"> </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: 20px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:20px;"> </td></tr><tr style="height: 20px"><td colspan="2" style="width: 485px; text-align:left;border-color:#000000;min-width:485px;">Federal statutory tax rate</td><td style="width: 90px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 35.0</td><td style="width: 20px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 35.0</td><td style="width: 20px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:20px;">%</td></tr><tr style="height: 20px"><td colspan="2" style="width: 485px; text-align:left;border-color:#000000;min-width:485px;">Increase (decrease):</td><td style="width: 90px; text-align:left;border-color:#000000;min-width:90px;"> </td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; text-align:left;border-color:#000000;min-width:90px;"> </td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;">Current state statutory income tax rate, net of federal tax benefit</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> 4.8</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> 4.5</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;">Amortization of investment and energy tax credits</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> (0.4)</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> (0.4)</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;">Differences required to be flowed-through by regulatory commissions</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> 1.2</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> (0.1)</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;">Gains on company and trust-owned life insurance</td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> (0.8)</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; text-align:right;border-color:#000000;min-width:90px;"> (1.4)</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;">%</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 470px; text-align:left;border-color:#000000;min-width:470px;">Other - net</td><td style="width: 90px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 0.5</td><td style="width: 20px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:90px;"> 0.4</td><td style="width: 20px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:20px;">%</td></tr><tr style="height: 21px"><td colspan="2" style="width: 485px; text-align:left;border-color:#000000;min-width:485px;">Effective tax rate</td><td style="width: 90px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:right;border-color:#000000;min-width:90px;"> 40.3</td><td style="width: 20px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:left;border-color:#000000;min-width:20px;">%</td><td style="width: 20px; text-align:left;border-color:#000000;min-width:20px;"> </td><td style="width: 90px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:right;border-color:#000000;min-width:90px;"> 38.0</td><td style="width: 20px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:left;border-color:#000000;min-width:20px;">%</td></tr></table></div>The increase in our effective tax rate for the nine months ended September 30, 2010 compared to the same period in 2009 was primarily due to an increase in the amortization rate of our regulatory tax asset pursuant to a regulatory order effective November 1, 2009, which we recover in utility rates. 7.        Income Tax The effective income tax rate for the nine months ended September 30, 2010 and 2009 varied from false false false us-types:textBlockItemType textblock Description containing the entire income tax disclosure. Examples include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information. This element may be used as a single block of text to encapsulate the entire disclosure including data and tables. 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