TargetHedgeAchieved

No definition available.

Name:	nwn_TargetHedgeAchieved
Namespace Prefix:	nwn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624258-113959

+ Details

Name:	us-gaap_CollateralAlreadyPostedAggregateFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal number of units used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_FairValueByAssetClassAxis=nwn_CollateralPostedwithNWNaturalCounterpartiesMember
Namespace Prefix:
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- Details

Name:	dei_LegalEntityAxis=nwn_NorthwestNaturalGasCompanyMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=nwn_FinancialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	nwn_GasYearAxis=nwn_GasYear20192020Member
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- Details

Name:	nwn_GasYearAxis=nwn_GasYear20202021Member
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=nwn_PhysicalMember
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- Details

Name:	us-gaap_UnderlyingAssetClassAxis=nwn_NaturalGasThermsMember
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Derivative Instruments Notional Amounts therm in Thousands	Mar. 31, 2021 USD ($) therm	Dec. 31, 2020 USD ($) therm	Mar. 31, 2020 USD ($) therm
Collateral Posted with NW Natural Counterparties [Member]
Derivative [Line Items]
Additional Collateral, Aggregate Fair Value \| $	$ 0		$ 0
Northwest Natural Gas Company [Member] \| Financial [Member] \| Gas Year 2019 - 2020 [Member]
Derivative [Line Items]
TargetHedgeAchieved	52.00%
Northwest Natural Gas Company [Member] \| Financial [Member] \| Gas Year 2020 - 2021
Derivative [Line Items]
TargetHedgeAchieved	53.00%
Northwest Natural Gas Company [Member] \| Physical [Member] \| Gas Year 2019 - 2020 [Member]
Derivative [Line Items]
TargetHedgeAchieved	19.00%
Northwest Natural Gas Company [Member] \| Physical [Member] \| Gas Year 2020 - 2021
Derivative [Line Items]
TargetHedgeAchieved	17.00%
Northwest Natural Gas Company [Member] \| Natural Gas Therms [Member] \| Financial [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount \| therm	597,495	784,400	487,420
Northwest Natural Gas Company [Member] \| Natural Gas Therms [Member] \| Physical [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount \| therm	187,595	457,593	369,450
Northwest Natural Gas Company [Member] \| Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount \| $	$ 5,954,000	$ 5,896,000	$ 9,885,000