Leases - Lease Asset and Liabilities - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	$ 72,096	$ 73,754	$ 72,096	$ 73,754	$ 73,429
Operating lease liabilities current liabilities	1,732	1,315	1,732	1,315	1,514
Operating lease liabilities noncurrent liabilities	77,951	78,826	77,951	78,826	78,965
Total operating lease liabilities	$ 79,683	$ 80,141	$ 79,683	$ 80,141	$ 80,479
Operating Lease, Weighted Average Remaining Lease Term	16 years 9 months 18 days	17 years 8 months 12 days	16 years 9 months 18 days	17 years 8 months 12 days	17 years 2 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	7.30%	7.20%	7.30%	7.20%	7.30%
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 142,659		$ 142,659
Regulatory Assets, Noncurrent	307,999	$ 301,855	307,999	$ 301,855	$ 340,432
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	3,693		3,693
Lessee, Operating Lease, Liability, to be Paid, Year One	7,469		7,469
Lessee, Operating Lease, Liability, Payments, Due Year Two	7,348		7,348
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,501		7,501
Lessee, Operating Lease, Liability, Payments, Due Year Four	7,645		7,645
Lessee, Operating Lease, Liability, Payments, Due after Year Five	109,003		109,003
Lessee, Operating Lease, Liability, Payments, Due	142,659		142,659
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	62,976		62,976
Total operating lease liabilities	79,683	80,141	79,683	80,141	80,479
Operating lease liabilities current liabilities	1,732	1,315	1,732	1,315	1,514
Operating lease liabilities noncurrent liabilities	77,951	78,826	77,951	78,826	78,965
Finance Lease, Liability, Payments, Due Next Twelve Months	0	100	0	100	0
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	1,837	1,739	3,643	3,478
Finance Lease, Principal Payments	0	307	173	382
nwn:Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		(14)
Operating leases	81		81	0
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	0	120	263	220
Finance Leases [Abstract]
Finance Lease, Liability	0		0
Finance Lease, Right-of-Use Asset	2,400	2,300	2,400	2,300	2,300
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	588	48	588	48	709
Operating lease liabilities current liabilities	134	17	134	17	151
Operating lease liabilities noncurrent liabilities	461	37	461	37	620
Total operating lease liabilities	595	54	595	54	771
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	659		659
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	83		83
Lessee, Operating Lease, Liability, to be Paid, Year One	162		162
Lessee, Operating Lease, Liability, Payments, Due Year Two	155		155
Lessee, Operating Lease, Liability, Payments, Due Year Three	140		140
Lessee, Operating Lease, Liability, Payments, Due Year Four	107		107
Lessee, Operating Lease, Liability, Payments, Due after Year Five	12		12
Lessee, Operating Lease, Liability, Payments, Due	659		659
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	64		64
Total operating lease liabilities	595	54	595	54	771
Operating lease liabilities current liabilities	134	17	134	17	151
Operating lease liabilities noncurrent liabilities	461	37	461	37	620
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	39	6	78	12
Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	71,508	73,706	71,508	73,706	72,720
Operating lease liabilities current liabilities	1,598	1,298	1,598	1,298	1,363
Operating lease liabilities noncurrent liabilities	77,490	78,789	77,490	78,789	78,345
Total operating lease liabilities	79,088	80,087	79,088	80,087	79,708
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	142,000		142,000
Regulatory Assets, Noncurrent	307,974	301,790	307,974	301,790	340,407
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	3,610		3,610
Lessee, Operating Lease, Liability, to be Paid, Year One	7,307		7,307
Lessee, Operating Lease, Liability, Payments, Due Year Two	7,193		7,193
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,361		7,361
Lessee, Operating Lease, Liability, Payments, Due Year Four	7,538		7,538
Lessee, Operating Lease, Liability, Payments, Due after Year Five	108,991		108,991
Lessee, Operating Lease, Liability, Payments, Due	142,000		142,000
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	62,912		62,912
Total operating lease liabilities	79,088	80,087	79,088	80,087	79,708
Operating lease liabilities current liabilities	1,598	1,298	1,598	1,298	1,363
Operating lease liabilities noncurrent liabilities	77,490	78,789	77,490	78,789	78,345
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	1,798	1,733	3,565	3,466
Finance Lease, Principal Payments	0	307	173	382
nwn:Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		(14)
Operating leases	81		81	0
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	$ 0	120	173	220
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Leases Cash Flow [Abstract]
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability			$ 90	0
New Headquarters Lease [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Term of Contract	20 years		20 years
Regulatory Assets, Noncurrent	$ 7,500	$ 6,300	$ 7,500	$ 6,300	$ 6,900
New Headquarters Lease Renewal Term 2 of 2 [Member] | New Headquarters Lease [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Renewal Term	7 years		7 years
New Headquarters Lease Renewal Term 1 of 2 [Member] | New Headquarters Lease [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Renewal Term	7 years		7 years
Maximum [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Term of Contract	17 years		17 years