Leases - Lease Asset and Liabilities - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	$ 76,957	$ 79,522	$ 77,446
Operating lease liabilities current liabilities	1,213	1,071	1,105
Operating lease liabilities noncurrent liabilities	80,414	79,105	80,621
Total operating lease liabilities	$ 81,627	$ 80,176	$ 81,726
Operating Lease, Weighted Average Remaining Lease Term	18 years 10 months 24 days	19 years 8 months 12 days	19 years 2 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	7.22%	7.20%	7.23%
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 5,202
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,992
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,156
Lessee, Operating Lease, Liability, Payments, Due Year Four	7,191
Lessee, Operating Lease, Liability, Payments, Due after Year Five	123,808
Lessee, Operating Lease, Liability, Payments, Due	157,306
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	75,679
Total operating lease liabilities	81,627	$ 80,176	$ 81,726
Operating lease liabilities current liabilities	1,213	1,071	1,105
Operating lease liabilities noncurrent liabilities	80,414	79,105	80,621
Finance Lease, Liability, Payments, Due Next Twelve Months	300
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	157,306
Regulatory Assets, Noncurrent	338,692	328,024	348,927
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	1,685	1,248
Finance Lease, Principal Payments	544	155
Operating leases	154	77,988
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	74	233
Finance Leases [Abstract]
Finance Lease, Right-of-Use Asset	1,900	700	1,800
Finance Lease, Liability	0
Lessee, Operating Lease, Liability, to be Paid, Year One	6,957
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	100	139	118
Operating lease liabilities current liabilities	46	87	51
Operating lease liabilities noncurrent liabilities	56	53	62
Total operating lease liabilities	102	140	113
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	41
Lessee, Operating Lease, Liability, Payments, Due Year Two	6
Lessee, Operating Lease, Liability, Payments, Due Year Three	6
Lessee, Operating Lease, Liability, Payments, Due Year Four	6
Lessee, Operating Lease, Liability, Payments, Due after Year Five	24
Lessee, Operating Lease, Liability, Payments, Due	107
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	5
Total operating lease liabilities	102	140	113
Operating lease liabilities current liabilities	46	87	51
Operating lease liabilities noncurrent liabilities	56	53	62
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	107
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	16	52
Finance Leases [Abstract]
Lessee, Operating Lease, Liability, to be Paid, Year One	24
Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	76,857	79,383	77,328
Operating lease liabilities current liabilities	1,167	984	1,054
Operating lease liabilities noncurrent liabilities	80,358	79,052	80,559
Total operating lease liabilities	81,525	80,036	81,613
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	5,161
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,986
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,150
Lessee, Operating Lease, Liability, Payments, Due Year Four	7,185
Lessee, Operating Lease, Liability, Payments, Due after Year Five	123,784
Lessee, Operating Lease, Liability, Payments, Due	157,199
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	75,674
Total operating lease liabilities	81,525	80,036	81,613
Operating lease liabilities current liabilities	1,167	984	1,054
Operating lease liabilities noncurrent liabilities	80,358	79,052	80,559
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	157,199
Regulatory Assets, Noncurrent	338,652	328,024	348,887
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	1,669	1,196
Finance Lease, Principal Payments	544	155
Operating leases	154	77,988
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	74	233
Finance Leases [Abstract]
Lessee, Operating Lease, Liability, to be Paid, Year One	6,933
New Headquarters Lease [Member]
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 159,400
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	20 years
Lessee, Operating Lease, Liability, Payments, Due	$ 159,400
Regulatory Assets, Noncurrent	$ 4,600	$ 600	$ 4,200
New Headquarters Lease Renewal Term 2 of 2 [Member] | New Headquarters Lease [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Renewal Term	7 years
New Headquarters Lease Renewal Term 1 of 2 [Member] | New Headquarters Lease [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Renewal Term	7 years