Significant Accounting Policies - Regulatory Liability Disclosure - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 103,210	$ 50,362	$ 41,126
Regulatory Liability, Noncurrent	645,046	639,663	632,400
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	869	870	869
Northwest Natural Gas Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	103,210	50,362	41,126
Regulatory Liability, Noncurrent	644,177	638,793	631,531
Northwest Natural Gas Company [Member] | Gas costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	1,519	1,118	3,767
Regulatory Liability, Noncurrent	101	314	538
Northwest Natural Gas Company [Member] | Deferred Derivative Gain (Loss) [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	46,168	13,674	5,950
Regulatory Liability, Noncurrent	7,912	6,135	3,958
Northwest Natural Gas Company [Member] | Decoupling [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	5,821	11,793	11,498
Regulatory Liability, Noncurrent	652	1,723	2,108
Northwest Natural Gas Company [Member] | Income taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	8,217	8,217	7,098
Regulatory Liability, Noncurrent	182,977	189,587	193,414
Northwest Natural Gas Company [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	2,137	5,262	5,697
Regulatory Liability, Noncurrent	12,850	13,074	16,794
Northwest Natural Gas Company [Member] | Accrued asset removal costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	439,685	427,960	414,719
Northwest Natural Gas Company [Member] | Asset Optimization Revenue Sharing
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 39,348	$ 10,298	$ 7,116