2.2.0.7 false Capital Stock 01200 - Disclosure - Capital Stock 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 Capital Stock [Abstract] 0 nwn_DisclosureCapitalStockAbstract 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 Capital Stock 1 us-gaap_ScheduleOfStockByClassTextBlock 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 3.       Capital Stock As of September 30, 2010, our common shares authorized were 100,000,000 and our outstanding shares were 26,640,453. We have a share repurchase program for our common stock under which we may purchase shares on the open market or through privately negotiated transactions. We currently have Board authorization through May 31, 2011 to repurchase up to an aggregate of 2.8 million shares or up to $100 million. No shares of common stock were repurchased under this program during the nine months ended September 30, 2010.  To date, a total of 2.1 million shares have been repurchased at a total cost of $83.3 million under the existing share repurchase program. 3.       Capital Stock As of September 30, 2010, our common shares authorized were 100,000,000 and our outstanding false false false us-types:textBlockItemType textblock This element is used to capture the complete disclosure pertaining to an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation. Stock by Class includes common, convertible and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued and outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 30 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 150 -Paragraph 9 false 1 2 false UnKnown UnKnown UnKnown false true