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    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Sep. 30, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '3 Months Ended
Mar. 31, 2012'</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 '9 Months Ended
Sep. 30, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2010'</Log>
    <Log type="Info">Process Flow-Through: 1001501 - Statement - Consolidated Statements of Comprehensive Income (Parentheticals)</Log>
    <Log type="Info">Process Flow-Through: 1002000 - Statement - Consolidated Balance Sheets</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2013'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Sep. 30, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Sep. 30, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Jun. 30, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Mar. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 1002501 - Statement - Consolidated Balance Sheets (Parentheticals)</Log>
    <Log type="Info">Process Flow-Through: 1003000 - Statement - Consolidated Statement of Cash Flows</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2011'</Log>
    <Log type="Info">	Process Flow-Through: Removing column '12 Months Ended
Dec. 31, 2010'</Log>
  </Logs>
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    <File>nwn-20130630.xml</File>
    <File>nwn-20130630.xsd</File>
    <File>nwn-20130630_cal.xml</File>
    <File>nwn-20130630_def.xml</File>
    <File>nwn-20130630_lab.xml</File>
    <File>nwn-20130630_pre.xml</File>
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</FilingSummary>
