Long-Term Debt - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term Debt	$ 955,919	$ 954,164	$ 955,425
Unamortized debt issuance costs	$ 7,364	7,554	7,480
Ratio of Indebtedness to Net Capital	0.560
Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 917,336	917,146	917,220
Unamortized debt issuance costs	$ 7,364	7,554	$ 7,480
Weighted average interest rate	4.60%
Northwest Natural Gas Company [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rate	2.82%
Northwest Natural Gas Company [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rate	9.05%
Two-year Term Loan Due 2021 [Member]
Debt Instrument [Line Items]
Stated interest rate	0.66%
Proceeds from Issuance of Debt		$ 35,000
Debt Instrument Covenant Consolidated Indebtedness to Capitalization Ratio	70.00%

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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No definition available.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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- Definition

Weighted average interest rate of long-term debt outstanding calculated at point in time.

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- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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Indebtedness divided by net capital.

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No definition available.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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