Significant Accounting Policies - Credit Losses - ASU 2016-13 $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($) numberOfLeases	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Number of Net Investments in Sales-Type Leases | numberOfLeases	2
Sales-type Lease, Net Investment in Lease, Allowance for Credit Loss	$ 0
Regulatory Assets, Noncurrent	312,665	$ 340,432	$ 301,660
Other Northwest Holdings [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	227	217
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	10
Accounts Receivable, Allowance for Credit Loss, Recovery	0
Northwest Holdings [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	2,312	3,296
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	1,973
Accounts Receivable, Allowance for Credit Loss, Recovery	(2,957)
Northwest Natural Gas Company [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	2,085	3,079
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	1,963
Accounts Receivable, Allowance for Credit Loss, Recovery	(2,957)
Regulatory Assets, Noncurrent	312,640	340,407	$ 301,596
Residential [Member] | Northwest Natural Gas Company [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	1,489	2,155
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	1,802
Accounts Receivable, Allowance for Credit Loss, Recovery	(2,468)
Commercial [Member] | Northwest Natural Gas Company [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	292	400
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	264
Accounts Receivable, Allowance for Credit Loss, Recovery	(372)
Industrial [Member] | Northwest Natural Gas Company [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	82	188
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	(105)
Accounts Receivable, Allowance for Credit Loss, Recovery	(1)
Accrued unbilled and other [Member] | Northwest Natural Gas Company [Member]
Accounts Receivable, Noncurrent, Credit Quality Indicator [Line Items]
Accounts Receivable, Allowance for Credit Loss	222	$ 336
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	2
Accounts Receivable, Allowance for Credit Loss, Recovery	$ (116)