Debt Fair Value of Long Term Debt - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Debt Instrument [Line Items]
Gross long-term debt	$ 962,994	$ 886,776	$ 906,757
Unamortized debt issuance costs	(7,586)	(5,712)	(6,072)
Carrying amount	955,408	881,064	900,685
Estimated fair value	1,118,565	957,268	997,096
Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Gross long-term debt	924,700	849,700	869,700
Unamortized debt issuance costs	(7,586)	(5,712)	(6,072)
Carrying amount	917,114	843,988	863,628
Estimated fair value	$ 1,080,663	$ 919,835	$ 959,906

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

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-Publisher FASB
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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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-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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