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

The percenage of pre-tax income from gas storage credited to a deferred regulatory account for crediting back to core utility customers when the costs of the capacity have been included in utility rates.

No definition available.

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

The percenage of pre-tax income from gas storage retained when the costs of the capacity have been included in utility rates.

No definition available.

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

The percenage of pre-tax income from gas storage retained when the costs of the capacity have not been included in utility rates.

No definition available.

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

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.

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

Name:	srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_StatementGeographicalAxis=stpr_OR
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dei_LegalEntityAxis=nwn_NorthwestHoldingsandNorthwestNaturalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: