Environmental Matters - Regulatory Deferred Assets - USD ($)	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Site Contingency [Line Items]
Regulatory Assets, Current	$ 60,672,000	$ 31,745,000	$ 30,021,000
Regulatory Assets, Noncurrent	$ 330,710,000	$ 348,927,000	$ 324,358,000
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	60,672,000	31,745,000	30,021,000
Regulatory Assets, Noncurrent	330,670,000	348,887,000	324,320,000
Northwest Natural Gas Company [Member] | Environmental costs [Member]
Site Contingency [Line Items]
Deferred costs and interest	50,604,000	44,516,000	42,098,000
Accrued site liabilities	110,237,000	120,352,000	124,981,000
Insurance proceeds and interest	(69,730,000)	(69,253,000)	(81,146,000)
Regulatory Assets	91,111,000	95,615,000	85,933,000
Regulatory Assets, Current	5,688,000	4,992,000	4,176,000
Regulatory Assets, Noncurrent	$ 85,423,000	$ 90,623,000	$ 81,757,000