Cost Incurred, Studies and Design Costs

No definition available.

Name:	nwn_CostIncurredStudiesandDesignCosts
Namespace Prefix:	nwn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

NRD Liability Claim Yakama Nation

+ References

No definition available.

+ Details

Name:	nwn_NRDLiabilityClaimYakamaNation
Namespace Prefix:	nwn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of Amended Complaints Filed

+ References

No definition available.

+ Details

Name:	nwn_NumberofAmendedComplaintsFiled
Namespace Prefix:	nwn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Proposed Remediation Plan, Clean-Up Costs

+ References

No definition available.

+ Details

Name:	nwn_ProposedRemediationPlanCleanUpCosts
Namespace Prefix:	nwn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Proposed Remediation Plan, Percentage of Clean-Up Costs

+ References

No definition available.

+ Details

Name:	nwn_ProposedRemediationPlanPercentageofCleanUpCosts
Namespace Prefix:	nwn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Site Contingency, Number of Other Third-Party Defendants

+ References

No definition available.

+ Details

Name:	nwn_SiteContingencyNumberofOtherThirdPartyDefendants
Namespace Prefix:	nwn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Site Contingency, Number of Potentially Responsible Parties

+ References

No definition available.

+ Details

Name:	nwn_SiteContingencyNumberofPotentiallyResponsibleParties
Namespace Prefix:	nwn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Site Contingency, Number of Remediation Projects

+ References

No definition available.

+ Details

Name:	nwn_SiteContingencyNumberofRemediationProjects
Namespace Prefix:	nwn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Site contingency: number of management pieces

+ References

No definition available.

+ Details

Name:	nwn_Sitecontingencynumberofmanagementpieces
Namespace Prefix:	nwn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Trustee Council Members - Number of Claimants

+ References

No definition available.

+ Details

Name:	nwn_TrusteeCouncilMembersNumberofClaimants
Namespace Prefix:	nwn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI https://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 55
-Paragraph 11
-URI https://asc.fasb.org/extlink&oid=6571209&loc=d3e13644-110860

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (d)(1)
-URI https://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

+ Details

Name:	us-gaap_AccruedEnvironmentalLossContingenciesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable after twelve months or beyond the next operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (d)(1)
-URI https://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI https://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

+ Details

Name:	us-gaap_AccruedEnvironmentalLossContingenciesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total anticipated costs associated with remediation, site restoration, postclosure, monitoring commitments, or other exit costs that may occur on the sale, disposal, or abandonment of a particular property resulting from unanticipated contamination of the assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.Y.Q4)
-URI https://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_EnvironmentalExitCostsAnticipatedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of the liability for remediation, site restoration, postclosure, monitoring commitments, or other exit costs associated with the sale, disposal or abandonment of a particular property resulting from unanticipated contamination of the assets.

+ References

+ Details

Name:	us-gaap_EnvironmentalExitCostsCostsAccruedToDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_SiteContingencyLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_GascoSiltronicSedimentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_PortlandHarborOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_GascoUplandsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_GascoSiltronicUplandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_FrontStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_OregonSteelMillsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=nwn_PortlandHarborMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=nwn_YakamaNationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Environmental Matters - Environmental Sites $ in Thousands	1 Months Ended	6 Months Ended
Environmental Matters - Environmental Sites $ in Thousands	Jan. 31, 2017 USD ($)	Jun. 30, 2022 USD ($) party property	Dec. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)
Site Contingency [Line Items]
Current Liabilities		$ 20,092	$ 26,985	$ 22,514
Non-Current Liabilities		84,752	88,851	87,795
Gasco/Siltronic Sediments
Site Contingency [Line Items]
Current Liabilities		6,144	7,582	6,658
Non-Current Liabilities		40,740	42,076	41,652
Site Contingency, Environmental Remediation Costs Recognized		46,900
Gasco/Siltronic Sediments \| Minimum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost		46,900
Gasco/Siltronic Sediments \| Maximum [Member]
Site Contingency [Line Items]
Environmental Exit Costs, Anticipated Cost		350,000
Portland Harbor Other [Member]
Site Contingency [Line Items]
Current Liabilities		2,313	2,592	2,195
Non-Current Liabilities		$ 8,613	9,570	6,588
Gasco Uplands [Member]
Site Contingency [Line Items]
Site contingency: number of management pieces		2
Gasco/Siltronic Upland [Member]
Site Contingency [Line Items]
Current Liabilities		$ 11,050	15,711	12,442
Non-Current Liabilities		34,352	36,215	38,401
Front Street [Member]
Site Contingency [Line Items]
Current Liabilities		585	1,100	1,219
Non-Current Liabilities		868	811	975
Additional studies and design costs		1,500
Oregon Steel Mills [Member]
Site Contingency [Line Items]
Current Liabilities		0	0	0
Non-Current Liabilities		$ 179	$ 179	$ 179
Portland Harbor [Member]
Site Contingency [Line Items]
Number of potentially responsible parties (more than) \| party		100
EPA final feasibility study and proposed remediation plan, clean-up costs, portland harbor	$ 1,050,000
Number of remediation projects \| property		2
Portland Harbor [Member] \| Minimum [Member]
Site Contingency [Line Items]
Percentage of clean-up costs	(30.00%)
Portland Harbor [Member] \| Maximum [Member]
Site Contingency [Line Items]
Percentage of clean-up costs	50.00%
Yakama Nation [Member] \| Portland Harbor Other [Member]
Site Contingency [Line Items]
Trustee Council Members - Number of Claimants		1
Site Contingency, Number of Other Third-Party Defendants		29
NRD liability claim yakama nation		$ 300
Number of Amended Complaints Filed		2