Environmental Matters - Regulatory Deferred Assets - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Site Contingency [Line Items]
Regulatory Assets, Current	$ 47,789,000	$ 31,745,000	$ 37,815,000
Regulatory Assets, Noncurrent	$ 338,692,000	$ 348,927,000	$ 328,024,000
Remediation Non-recovery Percentage	3.30%	3.30%	3.30%
Annual tariff rider collection	$ 5,000,000.0
Annual insurance proceeds to apply against remediation costs	5,000,000.0
Total annual remediation expense and interest	$ 10,000,000.0
Oregon [Member]
Site Contingency [Line Items]
Remediation Recovery Percentage	96.70%
Front Street [Member] | Environmental costs [Member]
Site Contingency [Line Items]
Accrued site liabilities	$ 100,000	$ 0.2	$ 400,000
Northwest Natural Gas Company [Member]
Site Contingency [Line Items]
Regulatory Assets, Current	47,789,000	31,745,000	37,815,000
Regulatory Assets, Noncurrent	338,652,000	348,887,000	328,024,000
Northwest Natural Gas Company [Member] | Environmental costs [Member]
Site Contingency [Line Items]
Deferred costs and interest	46,409,000	44,516,000	37,586,000
Accrued site liabilities	113,456,000	120,352,000	129,977,000
Insurance proceeds and interest	(69,492,000)	(69,253,000)	(80,613,000)
Regulatory Assets	90,373,000	95,615,000	86,950,000
Regulatory Assets, Current	5,396,000	4,992,000	4,459,000
Regulatory Assets, Noncurrent	$ 84,977,000	$ 90,623,000	$ 82,491,000