Significant Accounting Policies - Regulatory Liability Disclosure - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 99,663	$ 84,962	$ 61,546
Regulatory Liability, Noncurrent	705,929	695,896	672,215
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	118	50	50
Regulatory Liability, Noncurrent	949	949	952
Northwest Natural Gas Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	99,545	84,912	61,496
Regulatory Liability, Noncurrent	704,980	694,947	671,263
Northwest Natural Gas Company [Member] \| Gas costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	33,491	6,375	5,603
Regulatory Liability, Noncurrent	5,939	8,556	731
Northwest Natural Gas Company [Member] \| Deferred Derivative Gain (Loss) [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	7,624	11,184	11,691
Regulatory Liability, Noncurrent	2,588	373	1,551
Northwest Natural Gas Company [Member] \| Decoupling [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	9,538	7,612	8,715
Regulatory Liability, Noncurrent	1,510	2,118	1,358
Northwest Natural Gas Company [Member] \| Income taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	4,726	4,726	5,158
Regulatory Liability, Noncurrent	166,063	169,485	170,318
Northwest Natural Gas Company [Member] \| Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	4,704	6,233	7,002
Regulatory Liability, Noncurrent	17,980	15,855	15,454
Northwest Natural Gas Company [Member] \| Accrued asset removal costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	510,900	496,235	481,851
Northwest Natural Gas Company [Member] \| Asset Optimization Revenue Sharing
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	8,994	31,583	23,327
Regulatory Liability, Noncurrent	0	2,325	0
Northwest Natural Gas Company [Member] \| Washington Climate Commitment Act compliance
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	30,468	$ 17,199	$ 0
Regulatory Liability	$ 18,600

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481854/980-405-25-1

+ Details

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

- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

+ Details

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

- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=us-gaap_OtherRegulatoryAssetsLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=us-gaap_AssetRecoverableGasCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=us-gaap_DeferredDerivativeGainLossMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=nwn_DecouplingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=us-gaap_DeferredIncomeTaxChargesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=us-gaap_RemovalCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=nwn_AssetOptimizationRevenueSharingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=nwn_WashingtonClimateCommitmentActComplianceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: