Debt Fair Value of Long Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Debt Instrument [Line Items]
Gross long-term debt	$ 961,784	$ 886,776	$ 916,832
Unamortized debt issuance costs	(7,688)	(5,712)	(6,435)
Carrying amount	954,096	881,064	910,397
Estimated fair value	1,135,349	957,268	970,205
Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Gross long-term debt	924,700	849,700	879,700
Unamortized debt issuance costs	(7,688)	(5,712)	(6,394)
Carrying amount	917,012	843,988	873,306
Estimated fair value	$ 1,097,188	$ 919,835	$ 933,167

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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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
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

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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.

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