Significant Accounting Policies - Regulatory Liability Disclosure - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 81,314	$ 50,362	$ 47,137
Regulatory Liability, Noncurrent	636,384	639,663	623,219
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	869	870	844
Northwest Natural Gas Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	81,314	50,362	47,137
Regulatory Liability, Noncurrent	635,515	638,793	622,375
Northwest Natural Gas Company [Member] | Gas costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	2,575	1,118	4,046
Regulatory Liability, Noncurrent	634	314	1,328
Northwest Natural Gas Company [Member] | Deferred Derivative Gain (Loss) [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	19,914	13,674	2,257
Regulatory Liability, Noncurrent	3,087	6,135	2,451
Northwest Natural Gas Company [Member] | Decoupling [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	10,134	11,793	11,203
Regulatory Liability, Noncurrent	2,652	1,723	4,784
Northwest Natural Gas Company [Member] | Income taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	8,217	8,217	7,522
Regulatory Liability, Noncurrent	182,511	189,587	192,644
Northwest Natural Gas Company [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	4,596	5,262	4,868
Regulatory Liability, Noncurrent	12,142	13,074	12,956
Northwest Natural Gas Company [Member] | Accrued asset removal costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	434,489	427,960	408,212
Northwest Natural Gas Company [Member] | Asset Optimization Revenue Sharing
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 35,878	$ 10,298	$ 17,241