3.10.0.1 html 311 315 1 false 109 0 false 7 false false R1.htm 0001000 - Document - Document and Entity Information Sheet http://www.nwnatural.com/role/DocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 1001000 - Statement - Consolidated Statements of Comprehensive Income (Unaudited) Sheet http://www.nwnatural.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnaudited Consolidated Statements of Comprehensive Income (Unaudited) Statements 2 false false R3.htm 1001501 - Statement - Consolidated Statements of Comprehensive Income (Unaudited) - Parenthetical Sheet http://www.nwnatural.com/role/ConsolidatedStatementsOfComprehensiveIncomeUnauditedParenthetical Consolidated Statements of Comprehensive Income (Unaudited) - Parenthetical Statements 3 false false R4.htm 1002000 - Statement - Consolidated Balance Sheets (Unaudited) Sheet http://www.nwnatural.com/role/ConsolidatedBalanceSheetsUnaudited Consolidated Balance Sheets (Unaudited) Statements 4 false false R5.htm 1002501 - Statement - Consolidated Balance Sheets (Unaudited) - Parenthetical Sheet http://www.nwnatural.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical Consolidated Balance Sheets (Unaudited) - Parenthetical Statements 5 false false R6.htm 1004000 - Statement - Consolidated Statement of Cash Flows (Unaudited) Sheet http://www.nwnatural.com/role/ConsolidatedStatementOfCashFlowsUnaudited Consolidated Statement of Cash Flows (Unaudited) Statements 6 false false R7.htm 1005000 - Statement - NW Holdings Balance Sheet (Unaudited) Statement Sheet http://www.nwnatural.com/role/NwHoldingsBalanceSheetUnauditedStatement NW Holdings Balance Sheet (Unaudited) Statement Statements 7 false false R8.htm 1006000 - Statement - NW Holdings Statement of Cash Flows (Unaudited) Statement Sheet http://www.nwnatural.com/role/NwHoldingsStatementOfCashFlowsUnauditedStatement NW Holdings Statement of Cash Flows (Unaudited) Statement Statements 8 false false R9.htm 2101100 - Disclosure - Organization and Principles of Consolidation Sheet http://www.nwnatural.com/role/OrganizationAndPrinciplesOfConsolidation Organization and Principles of Consolidation Notes 9 false false R10.htm 2101100 - Disclosure - Significant Accounting Policies Sheet http://www.nwnatural.com/role/SignificantAccountingPolicies Significant Accounting Policies Notes 10 false false R11.htm 2103100 - Disclosure - Earnings Per Share Sheet http://www.nwnatural.com/role/EarningsPerShare Earnings Per Share Notes 11 false false R12.htm 2104100 - Disclosure - Segment Information Sheet http://www.nwnatural.com/role/SegmentInformation Segment Information Notes 12 false false R13.htm 2105100 - Disclosure - Revenue Revenue Sheet http://www.nwnatural.com/role/RevenueRevenue Revenue Revenue Notes 13 false false R14.htm 2106100 - Disclosure - Stock-Based Compensation Sheet http://www.nwnatural.com/role/StockBasedCompensation Stock-Based Compensation Notes 14 false false R15.htm 2107100 - Disclosure - Debt Sheet http://www.nwnatural.com/role/Debt Debt Notes 15 false false R16.htm 2108100 - 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 2109100 - Disclosure - Income Tax Sheet http://www.nwnatural.com/role/IncomeTax Income Tax Notes 17 false false R18.htm 2110100 - Disclosure - Property, Plant and Equipment Sheet http://www.nwnatural.com/role/PropertyPlantAndEquipment Property, Plant and Equipment Notes 18 false false R19.htm 2111100 - Disclosure - Gas Reserves Sheet http://www.nwnatural.com/role/GasReserves Gas Reserves Notes 19 false false R20.htm 2112100 - Disclosure - Investments Sheet http://www.nwnatural.com/role/Investments Investments Notes 20 false false R21.htm 2113100 - Disclosure - Business Combinations Business Combinations (Notes) Notes http://www.nwnatural.com/role/BusinessCombinationsBusinessCombinationsNotes Business Combinations Business Combinations (Notes) Notes 21 false false R22.htm 2114100 - Disclosure - Derivative Instruments Sheet http://www.nwnatural.com/role/DerivativeInstruments Derivative Instruments Notes 22 false false R23.htm 2115100 - Disclosure - Environmental Matters Sheet http://www.nwnatural.com/role/EnvironmentalMatters Environmental Matters Notes 23 false false R24.htm 2118100 - Disclosure - Discontinued Operations Discontinued Operations (Notes) Notes http://www.nwnatural.com/role/DiscontinuedOperationsDiscontinuedOperationsNotes Discontinued Operations Discontinued Operations (Notes) Notes 24 false false R25.htm 2119100 - Disclosure - Subsequent Event (Notes) Notes http://www.nwnatural.com/role/SubsequentEventNotes Subsequent Event (Notes) Notes 25 false false R26.htm 2201201 - Disclosure - Significant Accounting Policies (Policies) Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesPolicies Significant Accounting Policies (Policies) Policies http://www.nwnatural.com/role/SignificantAccountingPolicies 26 false false R27.htm 2301302 - Disclosure - Significant Accounting Policies (Tables) Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesTables Significant Accounting Policies (Tables) Tables http://www.nwnatural.com/role/SignificantAccountingPolicies 27 false false R28.htm 2303301 - Disclosure - Earnings Per Share (Tables) Sheet http://www.nwnatural.com/role/EarningsPerShareTables Earnings Per Share (Tables) Tables http://www.nwnatural.com/role/EarningsPerShare 28 false false R29.htm 2304301 - Disclosure - Segment Reporting (Tables) Sheet http://www.nwnatural.com/role/SegmentReportingTables Segment Reporting (Tables) Tables 29 false false R30.htm 2305301 - Disclosure - Revenue Revenue (Tables) Sheet http://www.nwnatural.com/role/RevenueRevenueTables Revenue Revenue (Tables) Tables http://www.nwnatural.com/role/RevenueRevenue 30 false false R31.htm 2307301 - Disclosure - Debt (Tables) Sheet http://www.nwnatural.com/role/DebtTables Debt (Tables) Tables http://www.nwnatural.com/role/Debt 31 false false R32.htm 2308301 - Disclosure - Pension and Other Postretirement Benefit Costs (Tables) Sheet http://www.nwnatural.com/role/PensionAndOtherPostretirementBenefitCostsTables Pension and Other Postretirement Benefit Costs (Tables) Tables http://www.nwnatural.com/role/PensionAndOtherPostretirementBenefitCosts 32 false false R33.htm 2309301 - Disclosure - Income Tax (Tables) Sheet http://www.nwnatural.com/role/IncomeTaxTables Income Tax (Tables) Tables http://www.nwnatural.com/role/IncomeTax 33 false false R34.htm 2310301 - Disclosure - Property, Plant and Equipment (Tables) Sheet http://www.nwnatural.com/role/PropertyPlantAndEquipmentTables Property, Plant and Equipment (Tables) Tables http://www.nwnatural.com/role/PropertyPlantAndEquipment 34 false false R35.htm 2311301 - Disclosure - Gas Reserves (Tables) Sheet http://www.nwnatural.com/role/GasReservesTables Gas Reserves (Tables) Tables http://www.nwnatural.com/role/GasReserves 35 false false R36.htm 2314301 - Disclosure - Derivative Instruments (Tables) Sheet http://www.nwnatural.com/role/DerivativeInstrumentsTables Derivative Instruments (Tables) Tables http://www.nwnatural.com/role/DerivativeInstruments 36 false false R37.htm 2315301 - Disclosure - Environmental Matters (Tables) Sheet http://www.nwnatural.com/role/EnvironmentalMattersTables Environmental Matters (Tables) Tables http://www.nwnatural.com/role/EnvironmentalMatters 37 false false R38.htm 2318301 - Disclosure - Discontinued Operations Discontinued Operations (Tables) Sheet http://www.nwnatural.com/role/DiscontinuedOperationsDiscontinuedOperationsTables Discontinued Operations Discontinued Operations (Tables) Tables http://www.nwnatural.com/role/DiscontinuedOperationsDiscontinuedOperationsNotes 38 false false R39.htm 2401401 - Disclosure - Organization and Principles of Consolidation Organization and Principles of Consolidation (Details) Sheet http://www.nwnatural.com/role/OrganizationAndPrinciplesOfConsolidationOrganizationAndPrinciplesOfConsolidationDetails Organization and Principles of Consolidation Organization and Principles of Consolidation (Details) Details 39 false false R40.htm 2401403 - Disclosure - Significant Accounting Policies - Regulatory Asset Disclosure (Details) Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesRegulatoryAssetDisclosureDetails Significant Accounting Policies - Regulatory Asset Disclosure (Details) Details 40 false false R41.htm 2401404 - Disclosure - Significant Accounting Policies - Regulatory Liability Disclosure (Details) Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesRegulatoryLiabilityDisclosureDetails Significant Accounting Policies - Regulatory Liability Disclosure (Details) Details 41 false false R42.htm 2401405 - Disclosure - Significant Accounting Policies Retirement Benefits ASU 2017-07 (Details) Sheet http://www.nwnatural.com/role/SignificantAccountingPoliciesRetirementBenefitsAsu201707Details Significant Accounting Policies Retirement Benefits ASU 2017-07 (Details) Details 42 false false R43.htm 2401406 - Disclosure - Significant Accounting Policies 606 Revenue Adoption (Details) Sheet http://www.nwnatural.com/role/SignificantAccountingPolicies606RevenueAdoptionDetails Significant Accounting Policies 606 Revenue Adoption (Details) Details 43 false false R44.htm 2403402 - Disclosure - Earnings Per Share (Details) Sheet http://www.nwnatural.com/role/EarningsPerShareDetails Earnings Per Share (Details) Details http://www.nwnatural.com/role/EarningsPerShareTables 44 false false R45.htm 2404402 - Disclosure - Segment Information Segments Summary (Details) Sheet http://www.nwnatural.com/role/SegmentInformationSegmentsSummaryDetails Segment Information Segments Summary (Details) Details 45 false false R46.htm 2404403 - Disclosure - Segment Information (Details) Sheet http://www.nwnatural.com/role/SegmentInformationDetails Segment Information (Details) Details http://www.nwnatural.com/role/SegmentInformation 46 false false R47.htm 2404404 - Disclosure - Segment Information - Utility Margin (Details) Sheet http://www.nwnatural.com/role/SegmentInformationUtilityMarginDetails Segment Information - Utility Margin (Details) Details 47 false false R48.htm 2405402 - Disclosure - Revenue Disaggregation of Revenue (Details) Sheet http://www.nwnatural.com/role/RevenueDisaggregationOfRevenueDetails Revenue Disaggregation of Revenue (Details) Details 48 false false R49.htm 2405403 - Disclosure - Revenue Remaining Performance Obligation (Details) Sheet http://www.nwnatural.com/role/RevenueRemainingPerformanceObligationDetails Revenue Remaining Performance Obligation (Details) Details 49 false false R50.htm 2406401 - Disclosure - Stock-Based Compensation (Details) Sheet http://www.nwnatural.com/role/StockBasedCompensationDetails Stock-Based Compensation (Details) Details http://www.nwnatural.com/role/StockBasedCompensation 50 false false R51.htm 2407402 - Disclosure - Debt (Details) Sheet http://www.nwnatural.com/role/DebtDetails Debt (Details) Details http://www.nwnatural.com/role/DebtTables 51 false false R52.htm 2407403 - Disclosure - Debt Short-term Debt (Details) Sheet http://www.nwnatural.com/role/DebtShortTermDebtDetails Debt Short-term Debt (Details) Details 52 false false R53.htm 2407404 - Disclosure - Debt Fair Value of Long Term Debt (Details) Sheet http://www.nwnatural.com/role/DebtFairValueOfLongTermDebtDetails Debt Fair Value of Long Term Debt (Details) Details 53 false false R54.htm 2408402 - Disclosure - Pension and Other Postretirement Benefit Costs - Net Periodic Benefit Cost (Details) Sheet http://www.nwnatural.com/role/PensionAndOtherPostretirementBenefitCostsNetPeriodicBenefitCostDetails Pension and Other Postretirement Benefit Costs - Net Periodic Benefit Cost (Details) Details 54 false false R55.htm 2408403 - Disclosure - Pension and Other Postretirement Benefit Costs - Amounts Recognized in Accumulated Other Comprehensive Loss (Details) Sheet http://www.nwnatural.com/role/PensionAndOtherPostretirementBenefitCostsAmountsRecognizedInAccumulatedOtherComprehensiveLossDetails Pension and Other Postretirement Benefit Costs - Amounts Recognized in Accumulated Other Comprehensive Loss (Details) Details 55 false false R56.htm 2408404 - Disclosure - Pension and Other Postretirement Benefit Costs - Narrative (Details) Sheet http://www.nwnatural.com/role/PensionAndOtherPostretirementBenefitCostsNarrativeDetails Pension and Other Postretirement Benefit Costs - Narrative (Details) Details 56 false false R57.htm 2409402 - Disclosure - Income Tax (Details) Sheet http://www.nwnatural.com/role/IncomeTaxDetails Income Tax (Details) Details http://www.nwnatural.com/role/IncomeTaxTables 57 false false R58.htm 2410402 - Disclosure - Property, Plant and Equipment (Details) Sheet http://www.nwnatural.com/role/PropertyPlantAndEquipmentDetails Property, Plant and Equipment (Details) Details http://www.nwnatural.com/role/PropertyPlantAndEquipmentTables 58 false false R59.htm 2411402 - Disclosure - Gas Reserves (Details) Sheet http://www.nwnatural.com/role/GasReservesDetails Gas Reserves (Details) Details http://www.nwnatural.com/role/GasReservesTables 59 false false R60.htm 2411403 - Disclosure - Gas Reserves - Investment (Details) Sheet http://www.nwnatural.com/role/GasReservesInvestmentDetails Gas Reserves - Investment (Details) Details 60 false false R61.htm 2412401 - Disclosure - Investments (Details) Sheet http://www.nwnatural.com/role/InvestmentsDetails Investments (Details) Details http://www.nwnatural.com/role/Investments 61 false false R62.htm 2413402 - Disclosure - Business Combinations Business Combinations (Details) Sheet http://www.nwnatural.com/role/BusinessCombinationsBusinessCombinationsDetails Business Combinations Business Combinations (Details) Details http://www.nwnatural.com/role/BusinessCombinationsBusinessCombinationsNotes 62 false false R63.htm 2414402 - Disclosure - Derivative Instruments Notional Amounts (Details) Sheet http://www.nwnatural.com/role/DerivativeInstrumentsNotionalAmountsDetails Derivative Instruments Notional Amounts (Details) Details 63 false false R64.htm 2414403 - Disclosure - Derivative Instruments Fair Value (Details) Sheet http://www.nwnatural.com/role/DerivativeInstrumentsFairValueDetails Derivative Instruments Fair Value (Details) Details 64 false false R65.htm 2414404 - Disclosure - Unrealized and Realized Gain/Loss (Details) Sheet http://www.nwnatural.com/role/UnrealizedAndRealizedGainLossDetails Unrealized and Realized Gain/Loss (Details) Details 65 false false R66.htm 2414405 - Disclosure - Derivative Instruments Credit Rating (Details) Sheet http://www.nwnatural.com/role/DerivativeInstrumentsCreditRatingDetails Derivative Instruments Credit Rating (Details) Details 66 false false R67.htm 2415402 - Disclosure - Environmental Matters (Details) Sheet http://www.nwnatural.com/role/EnvironmentalMattersDetails Environmental Matters (Details) Details http://www.nwnatural.com/role/EnvironmentalMattersTables 67 false false R68.htm 2415403 - Disclosure - Environmental Matters - Environmental Sites (Details) Sheet http://www.nwnatural.com/role/EnvironmentalMattersEnvironmentalSitesDetails Environmental Matters - Environmental Sites (Details) Details 68 false false R69.htm 2415404 - Disclosure - Environmental Matters - Regulatory Deferred Assets (Details) Sheet http://www.nwnatural.com/role/EnvironmentalMattersRegulatoryDeferredAssetsDetails Environmental Matters - Regulatory Deferred Assets (Details) Details 69 false false R70.htm 2418402 - Disclosure - Discontinued Operations Discontinued Operations (Details) Sheet http://www.nwnatural.com/role/DiscontinuedOperationsDiscontinuedOperationsDetails Discontinued Operations Discontinued Operations (Details) Details http://www.nwnatural.com/role/DiscontinuedOperationsDiscontinuedOperationsTables 70 false false R71.htm 2418403 - Disclosure - Discontinued Operations Agreement (Details) Sheet http://www.nwnatural.com/role/DiscontinuedOperationsAgreementDetails Discontinued Operations Agreement (Details) Details 71 false false R72.htm 2419402 - Disclosure - Subsequent Event (Details) Sheet http://www.nwnatural.com/role/SubsequentEventDetails Subsequent Event (Details) Details http://www.nwnatural.com/role/SubsequentEventNotes 72 false false All Reports Book All Reports nwn-20180930.xml nwn-20180930.xsd nwn-20180930_cal.xml nwn-20180930_def.xml nwn-20180930_lab.xml nwn-20180930_pre.xml http://xbrl.sec.gov/dei/2014-01-31 http://xbrl.sec.gov/stpr/2011-01-31 http://xbrl.sec.gov/invest/2013-01-31 http://fasb.org/us-gaap/2017-01-31 true true