3.20.2 html 533 478 1 false 105 0 false 8 false false R1.htm 0001001 - Document - Document and Entity Information Sheet http://www.nwnatural.com/role/DocumentandEntityInformation Document and Entity Information Cover 1 false false R2.htm 1001002 - Statement - Consolidated Statements of Comprehensive Income Sheet http://www.nwnatural.com/role/ConsolidatedStatementsofComprehensiveIncome Consolidated Statements of Comprehensive Income Statements 2 false false R3.htm 1002003 - Statement - Consolidated Balance Sheets Sheet http://www.nwnatural.com/role/ConsolidatedBalanceSheets Consolidated Balance Sheets Statements 3 false false R4.htm 1003004 - Statement - Consolidated Statement of Shareholders' Equity Sheet http://www.nwnatural.com/role/ConsolidatedStatementofShareholdersEquity Consolidated Statement of Shareholders' Equity Statements 4 false false R5.htm 1004005 - Statement - Consolidated Statement of Cash Flows Sheet http://www.nwnatural.com/role/ConsolidatedStatementofCashFlows Consolidated Statement of Cash Flows Statements 5 false false R6.htm 1405415 - Statement - Debt Short-term Debt Sheet http://www.nwnatural.com/role/DebtShorttermDebt Debt Short-term Debt Statements 6 false false R7.htm 1406420 - Statement - Pension and Other Postretirement Benefit Costs - Narrative Sheet http://www.nwnatural.com/role/PensionandOtherPostretirementBenefitCostsNarrative Pension and Other Postretirement Benefit Costs - Narrative Statements 7 false false R8.htm 2101101 - Disclosure - Organization and Principles of Consolidation Sheet http://www.nwnatural.com/role/OrganizationandPrinciplesofConsolidation Organization and Principles of Consolidation Notes 8 false false R9.htm 2103102 - Disclosure - Significant Accounting Policies Sheet http://www.nwnatural.com/role/SignificantAccountingPolicies Significant Accounting Policies Notes 9 false false R10.htm 2109103 - Disclosure - Earnings Per Share Sheet http://www.nwnatural.com/role/EarningsPerShare Earnings Per Share Notes 10 false false R11.htm 2112104 - Disclosure - Segment Information Sheet http://www.nwnatural.com/role/SegmentInformation Segment Information Notes 11 false false R12.htm 2117105 - Disclosure - Revenue Sheet http://www.nwnatural.com/role/Revenue Revenue Notes 12 false false R13.htm 2121106 - Disclosure - Leases Sheet http://www.nwnatural.com/role/Leases Leases Notes 13 false false R14.htm 2126107 - Disclosure - Stock-Based Compensation Sheet http://www.nwnatural.com/role/StockBasedCompensation Stock-Based Compensation Notes 14 false false R15.htm 2128108 - Disclosure - Debt Sheet http://www.nwnatural.com/role/Debt Debt Notes 15 false false R16.htm 2132109 - Disclosure - Pension and Other Postretirement Benefit Costs Sheet http://www.nwnatural.com/role/PensionandOtherPostretirementBenefitCosts Pension and Other Postretirement Benefit Costs Notes 16 false false R17.htm 2136110 - Disclosure - Income Tax Sheet http://www.nwnatural.com/role/IncomeTax Income Tax Notes 17 false false R18.htm 2139111 - Disclosure - Property, Plant and Equipment Sheet http://www.nwnatural.com/role/PropertyPlantandEquipment Property, Plant and Equipment Notes 18 false false R19.htm 2142112 - Disclosure - Gas Reserves Sheet http://www.nwnatural.com/role/GasReserves Gas Reserves Notes 19 false false R20.htm 2146113 - Disclosure - Investments Sheet http://www.nwnatural.com/role/Investments Investments Notes 20 false false R21.htm 2148114 - Disclosure - Business Combinations Business Combinations Sheet http://www.nwnatural.com/role/BusinessCombinationsBusinessCombinations Business Combinations Business Combinations Notes 21 false false R22.htm 2151115 - Disclosure - Derivative Instruments Sheet http://www.nwnatural.com/role/DerivativeInstruments Derivative Instruments Notes 22 false false R23.htm 2157116 - Disclosure - Environmental Matters Sheet http://www.nwnatural.com/role/EnvironmentalMatters Environmental Matters Notes 23 false false R24.htm 2162117 - Disclosure - Discontinued Operations Sheet http://www.nwnatural.com/role/DiscontinuedOperations Discontinued Operations Notes 24 false false R25.htm 2204201 - Disclosure - Significant Accounting Policies Sheet http://www.nwnatural.com/role/SignificantAccountingPolicies_1 Significant Accounting Policies Notes 25 false false R26.htm 2305301 - Disclosure - Significant Accounting Policies Sheet http://www.nwnatural.com/role/SignificantAccountingPolicies_2 Significant Accounting Policies Notes 26 false false R27.htm 2310302 - Disclosure - Earnings Per Share Sheet http://www.nwnatural.com/role/EarningsPerShare_1 Earnings Per Share Notes 27 false false R28.htm 2313303 - Disclosure - Segment Information Sheet http://www.nwnatural.com/role/SegmentInformation_1 Segment Information Notes 28 false false R29.htm 2318304 - Disclosure - Revenue Sheet http://www.nwnatural.com/role/Revenue_1 Revenue Notes 29 false false R30.htm 2322305 - Disclosure - Leases Sheet http://www.nwnatural.com/role/Leases_1 Leases Notes 30 false false R31.htm 2329306 - Disclosure - Debt Sheet http://www.nwnatural.com/role/Debt_1 Debt Notes 31 false false R32.htm 2333307 - Disclosure - Pension and Other Postretirement Benefit Costs Sheet http://www.nwnatural.com/role/PensionandOtherPostretirementBenefitCosts_1 Pension and Other Postretirement Benefit Costs Notes 32 false false R33.htm 2337308 - Disclosure - Income Tax Sheet http://www.nwnatural.com/role/IncomeTax_1 Income Tax Notes 33 false false R34.htm 2340309 - Disclosure - Property, Plant and Equipment Sheet http://www.nwnatural.com/role/PropertyPlantandEquipment_1 Property, Plant and Equipment Notes 34 false false R35.htm 2343310 - Disclosure - Gas Reserves Sheet http://www.nwnatural.com/role/GasReserves_1 Gas Reserves Notes 35 false false R36.htm 2349311 - Disclosure - Business Combinations Business Combinations Sheet http://www.nwnatural.com/role/BusinessCombinationsBusinessCombinations_1 Business Combinations Business Combinations Notes 36 false false R37.htm 2352312 - Disclosure - Derivative Instruments Sheet http://www.nwnatural.com/role/DerivativeInstruments_1 Derivative Instruments Notes 37 false false R38.htm 2358313 - Disclosure - Environmental Matters Sheet http://www.nwnatural.com/role/EnvironmentalMatters_1 Environmental Matters Notes 38 false false R39.htm 2363314 - Disclosure - Discontinued Operations Sheet http://www.nwnatural.com/role/DiscontinuedOperations_1 Discontinued Operations Notes 39 false false R40.htm 2406402 - Disclosure - Significant Accounting Policies - Regulatory Asset Disclosure Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesRegulatoryAssetDisclosure Significant Accounting Policies - Regulatory Asset Disclosure Notes 40 false false R41.htm 2407403 - Disclosure - Significant Accounting Policies - Regulatory Liability Disclosure Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesRegulatoryLiabilityDisclosure Significant Accounting Policies - Regulatory Liability Disclosure Notes 41 false false R42.htm 2408404 - Disclosure - Significant Accounting Policies - Credit Losses - ASU 2016-13 Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesCreditLossesASU201613 Significant Accounting Policies - Credit Losses - ASU 2016-13 Notes 42 false false R43.htm 2411405 - Disclosure - Earnings Per Share Sheet http://www.nwnatural.com/role/EarningsPerShare_2 Earnings Per Share Notes 43 false false R44.htm 2414406 - Disclosure - Segment Information - Narrative Sheet http://www.nwnatural.com/role/SegmentInformationNarrative Segment Information - Narrative Notes 44 false false R45.htm 2415407 - Disclosure - Segment Information - Schedule of Summarized Financial Information by Segment Sheet http://www.nwnatural.com/role/SegmentInformationScheduleofSummarizedFinancialInformationbySegment Segment Information - Schedule of Summarized Financial Information by Segment Notes 45 false false R46.htm 2416408 - Disclosure - Segment Information - Additional Segment Information Sheet http://www.nwnatural.com/role/SegmentInformationAdditionalSegmentInformation Segment Information - Additional Segment Information Notes 46 false false R47.htm 2419409 - Disclosure - Revenue - Disaggregation of Revenue Sheet http://www.nwnatural.com/role/RevenueDisaggregationofRevenue Revenue - Disaggregation of Revenue Notes 47 false false R48.htm 2420410 - Disclosure - Revenue - Revenue, Remaining Performance Obligation Sheet http://www.nwnatural.com/role/RevenueRevenueRemainingPerformanceObligation Revenue - Revenue, Remaining Performance Obligation Notes 48 false false R49.htm 2423411 - Disclosure - Leases - Lease Revenue Sheet http://www.nwnatural.com/role/LeasesLeaseRevenue Leases - Lease Revenue Notes 49 false false R50.htm 2424412 - Disclosure - Leases - Lease Expense Sheet http://www.nwnatural.com/role/LeasesLeaseExpense Leases - Lease Expense Notes 50 false false R51.htm 2425413 - Disclosure - Leases - Lease Asset and Liabilities Sheet http://www.nwnatural.com/role/LeasesLeaseAssetandLiabilities Leases - Lease Asset and Liabilities Notes 51 false false R52.htm 2427414 - Disclosure - Stock-Based Compensation Sheet http://www.nwnatural.com/role/StockBasedCompensation_1 Stock-Based Compensation Notes 52 false false R53.htm 2430416 - Disclosure - Long-Term Debt Sheet http://www.nwnatural.com/role/LongTermDebt Long-Term Debt Notes 53 false false R54.htm 2431417 - Disclosure - Debt Fair Value of Long Term Debt Sheet http://www.nwnatural.com/role/DebtFairValueofLongTermDebt Debt Fair Value of Long Term Debt Notes 54 false false R55.htm 2434418 - Disclosure - Pension and Other Postretirement Benefit Costs - Net Periodic Benefit Cost Sheet http://www.nwnatural.com/role/PensionandOtherPostretirementBenefitCostsNetPeriodicBenefitCost Pension and Other Postretirement Benefit Costs - Net Periodic Benefit Cost Notes 55 false false R56.htm 2435419 - Disclosure - Pension and Other Postretirement Benefit Costs - Amounts Recognized in Accumulated Other Comprehensive Loss Sheet http://www.nwnatural.com/role/PensionandOtherPostretirementBenefitCostsAmountsRecognizedinAccumulatedOtherComprehensiveLoss Pension and Other Postretirement Benefit Costs - Amounts Recognized in Accumulated Other Comprehensive Loss Notes 56 false false R57.htm 2438421 - Disclosure - Income Tax Sheet http://www.nwnatural.com/role/IncomeTax_2 Income Tax Notes 57 false false R58.htm 2441422 - Disclosure - Property, Plant and Equipment Sheet http://www.nwnatural.com/role/PropertyPlantandEquipment_2 Property, Plant and Equipment Notes 58 false false R59.htm 2444423 - Disclosure - Gas Reserves Sheet http://www.nwnatural.com/role/GasReserves_2 Gas Reserves Notes 59 false false R60.htm 2445424 - Disclosure - Gas Reserves - Investment Sheet http://www.nwnatural.com/role/GasReservesInvestment Gas Reserves - Investment Notes 60 false false R61.htm 2447425 - Disclosure - Investments Sheet http://www.nwnatural.com/role/Investments_1 Investments Notes 61 false false R62.htm 2450426 - Disclosure - Business Combinations Business Combinations Sheet http://www.nwnatural.com/role/BusinessCombinationsBusinessCombinations_2 Business Combinations Business Combinations Notes 62 false false R63.htm 2453427 - Disclosure - Derivative Instruments Notional Amounts Sheet http://www.nwnatural.com/role/DerivativeInstrumentsNotionalAmounts Derivative Instruments Notional Amounts Notes 63 false false R64.htm 2454428 - Disclosure - Derivative Instruments Fair Value Sheet http://www.nwnatural.com/role/DerivativeInstrumentsFairValue Derivative Instruments Fair Value Notes 64 false false R65.htm 2455429 - Disclosure - Unrealized and Realized Gain/Loss Sheet http://www.nwnatural.com/role/UnrealizedandRealizedGainLoss Unrealized and Realized Gain/Loss Notes 65 false false R66.htm 2456430 - Disclosure - Derivative Instruments Credit Rating Sheet http://www.nwnatural.com/role/DerivativeInstrumentsCreditRating Derivative Instruments Credit Rating Notes 66 false false R67.htm 2459431 - Disclosure - Environmental Matters Sheet http://www.nwnatural.com/role/EnvironmentalMatters_2 Environmental Matters Notes 67 false false R68.htm 2460432 - Disclosure - Environmental Matters - Environmental Sites Sheet http://www.nwnatural.com/role/EnvironmentalMattersEnvironmentalSites Environmental Matters - Environmental Sites Notes 68 false false R69.htm 2461433 - Disclosure - Environmental Matters - Regulatory Deferred Assets Sheet http://www.nwnatural.com/role/EnvironmentalMattersRegulatoryDeferredAssets Environmental Matters - Regulatory Deferred Assets Notes 69 false false R70.htm 2464434 - Disclosure - Discontinued Operations Sheet http://www.nwnatural.com/role/DiscontinuedOperations_2 Discontinued Operations Notes 70 false false All Reports Book All Reports nwn-20200930.htm ex3112020q3ng.htm ex3122020q3ng.htm ex3132020q3ng.htm ex3142020q3ng.htm ex3212020q3ng.htm ex3222020q3ng.htm nwn-20200930.xsd nwn-20200930_cal.xml nwn-20200930_def.xml nwn-20200930_lab.xml nwn-20200930_pre.xml nwn-20200930_g1.jpg nwn-20200930_g2.jpg http://xbrl.sec.gov/stpr/2018-01-31 http://fasb.org/us-gaap/2019-01-31 http://xbrl.sec.gov/dei/2019-01-31 http://fasb.org/srt/2019-01-31 true true