2.2.0.25falsefalse10900 - Disclosure - Pension and Other Postretirement Benefitstruefalsefalse1falsefalseUSDfalsefalse1/1/2011 - 3/31/2011 USD ($) USD ($) / shares $FROM_Jan01_2011_TO_Mar31_2011http://www.sec.gov/CIK0000073020duration2011-01-01T00:00:002011-03-31T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDpershareDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0USDUSD$2true0nwn_DisclosurePensionAndOtherPostretirementBenefitsnwnfalsenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalseDisclosure - Pension and Other Postretirement Benefits3false0us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlockus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse009.       Pension and Other Postretirement Benefit Costs The following tables provide the components of net periodic benefit cost for our company-sponsored qualified and non-qualified defined benefit pension plans and other postretirement benefit plans:<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: 305px; text-align:left;border-color:#000000;min-width:305px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td colspan="11" style="width: 390px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:390px;">Three Months Ended March 31,</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 305px; text-align:left;border-color:#000000;min-width:305px;"> </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:center;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:center;border-color:#000000;min-width:80px;"> </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;text-align:center;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:center;border-color:#000000;min-width:80px;"> </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;text-align:center;border-color:#000000;min-width:10px;"> </td><td colspan="4" style="width: 180px; border-top-style:solid;border-top-width:1px;text-align:center;border-color:#000000;min-width:180px;">Other Postretirement</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 305px; text-align:left;border-color:#000000;min-width:305px;"> </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: 180px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:180px;">Pension Benefits</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: 180px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:180px;">Benefits</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:320px;">Thousands</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: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:80px;">2011</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:left;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:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:80px;">2010</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;border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:80px;">2011</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:left;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:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:80px;">2010</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:320px;">Service cost</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 1,899</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 1,773</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 168</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 156</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; text-align:left;border-color:#000000;min-width:320px;">Interest cost</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 4,527</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 4,491</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 344</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 343</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; text-align:left;border-color:#000000;min-width:320px;">Expected return on plan assets</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> (4,456)</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> (4,564)</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> -</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> -</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; text-align:left;border-color:#000000;min-width:320px;">Amortization of net actuarial loss</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 2,692</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 1,768</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 68</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 7</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; text-align:left;border-color:#000000;min-width:320px;">Amortization of prior service costs</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 88</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 206</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 49</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; text-align:right;border-color:#000000;min-width:80px;"> 49</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; text-align:left;border-color:#000000;min-width:320px;">Amortization of transition obligations</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> -</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> -</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 103</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 103</td></tr><tr style="height: 20px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 305px; text-align:left;border-color:#000000;min-width:305px;">Net periodic benefit cost</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:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 4,750</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:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 3,674</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:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 732</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:left;border-color:#000000;min-width:10px;"> </td><td style="width: 80px; border-top-style:solid;border-top-width:1px;text-align:right;border-color:#000000;min-width:80px;"> 658</td></tr><tr style="height: 20px"><td colspan="2" style="width: 320px; text-align:left;border-color:#000000;min-width:320px;">Amount allocated to construction</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> (1,235)</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> (953)</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> (226)</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 style="width: 80px; border-bottom-style:solid;border-bottom-width:1px;text-align:right;border-color:#000000;min-width:80px;"> (208)</td></tr><tr style="height: 21px"><td style="width: 15px; text-align:left;border-color:#000000;min-width:15px;"> </td><td style="width: 305px; text-align:left;border-color:#000000;min-width:305px;">Net amount charged to expense</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;border-bottom-style:double;border-bottom-width:3px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:right;border-color:#000000;min-width:80px;"> 3,515</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;border-bottom-style:double;border-bottom-width:3px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:right;border-color:#000000;min-width:80px;"> 2,721</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 10px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:right;border-color:#000000;min-width:80px;"> 506</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;border-bottom-style:double;border-bottom-width:3px;text-align:left;border-color:#000000;min-width:10px;">$</td><td style="width: 80px; border-top-style:solid;border-top-width:1px;border-bottom-style:double;border-bottom-width:3px;text-align:right;border-color:#000000;min-width:80px;"> 450</td></tr></table></div>See Part II, Item 8., Note 9, in the 2010 Form 10-K for more information about our pension and other postretirement benefit plans. In addition to the company-sponsored defined benefit plans referred to above, we contribute to a multiemployer pension plan for our bargaining unit employees in accordance with our collective bargaining agreement, known as the Western States Office and Professional Employees International Union Pension Fund (Western States Plan). The cost of this plan is in addition to pension expense in the table above. The Western States Plan has reported an accumulated funding deficit for the current plan year and remains in critical status. The Western States Plan trustees adopted a rehabilitation plan that reduced benefit accrual rates and adjustable benefits for active employee participants and increased future employer contribution rates. These changes are expected to improve the funding status of the plan.  We made contributions totaling $0.1 million to the Western States Plan for both the three months ended March 31, 2011 and 2010.  If we withdraw and the plan is underfunded, we could be assessed a withdrawal liability. Currently, we have no intent to withdraw from the plan, so we have not recorded a withdrawal liability. Employer Pension Contributions During the first quarter of 2011 we made cash contributions totaling $13.6 million to our qualified defined benefit pension plans. We also expect to contribute up to an additional $10 million to these qualified plans over the last nine months of 2011, plus we expect to make ongoing benefit payments under our unfunded, non-qualified pension plans and other postretirement benefit plans. For more information see Part II, Item 8., Note 9, in the 2010 Form 10-K.9.       Pension and Other Postretirement Benefit Costs The following tables provide the components of net periodicfalsefalsefalsefalsefalseOtherus-types:textBlockItemTypestringDescription containing the entire pension and other postretirement benefits disclosure as a single block of text.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS106-2 -Paragraph 20, 21, 22 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5, 6, 7, 8 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Implementation Guide (Q and A) -Number FAS88 -Paragraph 63 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 158 -Paragraph 7, 21, 22 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph b Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 30 -Paragraph 26 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 106 -Paragraph 518 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-2 -Paragraph 8 Reference 10: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 8 -Subparagraph m Reference 11: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph h Reference 12: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph a Reference 13: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph q falsefalsePension and Other Postretirement Benefits Text Block12Pension and Other Postretirement BenefitsUnKnownUnKnownUnKnownUnKnownfalsetrue