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    <Log type="Info">Element us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate had a mix of decimals attribute values: 2 3.</Log>
    <Log type="Info">'Monetary' elements on report '040200 - Disclosure - Summary of Significant Accounting Policies (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040400 - Disclosure - Segment Information (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Shares' elements on report '040500 - Disclosure - Common Stock (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040700 - Disclosure - Cost and Fair Value Basis of Long-Term Debt (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040900 - Disclosure - Pension and Other Postretirement Benefits (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '041000 - Disclosure - Income Tax (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '041100 - Disclosure - Property, Plant and Equipment (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '041200 - Disclosure - Gas Reserves and Other Investments (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '041300 - Disclosure - Derivative Instruments (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '041400 - Disclosure - Leases (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '041500 - Disclosure - Commitments and Contingencies (details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 010020 - Statement - Consolidated Statements of Income and Comprehensive Income</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2010'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2010'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Jun. 30, 2010'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2010'</Log>
    <Log type="Info">Process Flow-Through: 010025 - Statement - Consolidated Statements of Income and Comprehensive Income (parentheticals)</Log>
    <Log type="Info">Process Flow-Through: 010030 - Statement - Consolidated Balance Sheets</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2009'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2008'</Log>
    <Log type="Info">Process Flow-Through: 010040 - Statement - Consolidated Balance Sheets (Parentheticals)</Log>
    <Log type="Info">Process Flow-Through: 010050 - Statement - Consolidated Statement of Cash Flows</Log>
  </Logs>
  <InputFiles>
    <File>nwn-20111231.xml</File>
    <File>nwn-20111231.xsd</File>
    <File>nwn-20111231_cal.xml</File>
    <File>nwn-20111231_def.xml</File>
    <File>nwn-20111231_lab.xml</File>
    <File>nwn-20111231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
