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Environmental Matters - Regulatory Deferred Assets - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2024
Dec. 31, 2023
Jun. 30, 2023
Site Contingency [Line Items]      
Regulatory Assets, Current $ 124,102 $ 178,270 $ 111,819
Regulatory Assets, Noncurrent $ 308,521 $ 333,443 $ 307,999
Remediation Non-recovery Percentage 3.30% 3.30% 3.30%
Annual tariff rider collection $ 5,000    
Annual insurance proceeds to apply against remediation costs 5,000    
Total annual remediation expense and interest $ 10,000    
Oregon [Member]      
Site Contingency [Line Items]      
Remediation Recovery Percentage 96.70%    
Front Street [Member] | Environmental costs [Member]      
Site Contingency [Line Items]      
Accrued site liabilities $ 38 $ 53 $ 47
Northwest Natural Gas Company [Member]      
Site Contingency [Line Items]      
Regulatory Assets, Current 124,078 178,270 111,819
Regulatory Assets, Noncurrent 308,415 333,418 307,974
Northwest Natural Gas Company [Member] | Environmental costs [Member]      
Site Contingency [Line Items]      
Deferred costs and interest 64,917 57,758 51,237
Accrued site liabilities 109,212 121,575 109,727
Insurance proceeds and interest (52,025) (50,764) (56,055)
Regulatory Assets 122,104 128,569 104,909
Regulatory Assets, Current 9,915 9,950 6,749
Regulatory Assets, Noncurrent $ 112,189 $ 118,619 $ 98,160