Leases - Lease Asset and Liabilities - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	$ 76,294	$ 78,566	$ 76,294	$ 78,566	$ 77,446
Operating lease liabilities current liabilities	1,228	931	1,228	931	1,105
Operating lease liabilities noncurrent liabilities	80,088	80,159	80,088	80,159	80,621
Total operating lease liabilities	$ 81,316	$ 81,090	$ 81,316	$ 81,090	$ 81,726
Operating Lease, Weighted Average Remaining Lease Term	18 years 8 months 12 days	19 years 8 months 12 days	18 years 8 months 12 days	19 years 8 months 12 days	19 years 2 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	7.20%	7.20%	7.20%	7.20%	7.20%
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 155,574		$ 155,574
Regulatory Assets, Noncurrent	330,710	$ 324,358	330,710	$ 324,358	$ 348,927
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	3,470		3,470
Lessee, Operating Lease, Liability, to be Paid, Year One	6,957		6,957
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,992		6,992
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,156		7,156
Lessee, Operating Lease, Liability, Payments, Due Year Four	7,191		7,191
Lessee, Operating Lease, Liability, Payments, Due after Year Five	123,808		123,808
Lessee, Operating Lease, Liability, Payments, Due	155,574		155,574
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	74,258		74,258
Total operating lease liabilities	81,316	81,090	81,316	81,090	81,726
Operating lease liabilities current liabilities	1,228	931	1,228	931	1,105
Operating lease liabilities noncurrent liabilities	80,088	80,159	80,088	80,159	80,621
Finance Lease, Liability, Payments, Due Next Twelve Months	200		200
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	1,734	970	3,419	2,218
Finance Lease, Principal Payments	134	302	678	457
Operating leases	0	445	154	78,433
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	20	477	94	710
Finance Leases [Abstract]
Finance Lease, Right-of-Use Asset	1,900	1,100	1,900	1,100	1,800
Finance Lease, Liability	0		0
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	83	102	83	102	118
Operating lease liabilities current liabilities	35	63	35	63	51
Operating lease liabilities noncurrent liabilities	45	39	45	39	62
Total operating lease liabilities	80	102	80	102	113
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	91		91
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	25		25
Lessee, Operating Lease, Liability, to be Paid, Year One	24		24
Lessee, Operating Lease, Liability, Payments, Due Year Two	6		6
Lessee, Operating Lease, Liability, Payments, Due Year Three	6		6
Lessee, Operating Lease, Liability, Payments, Due Year Four	6		6
Lessee, Operating Lease, Liability, Payments, Due after Year Five	24		24
Lessee, Operating Lease, Liability, Payments, Due	91		91
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	11		11
Total operating lease liabilities	80	102	80	102	113
Operating lease liabilities current liabilities	35	63	35	63	51
Operating lease liabilities noncurrent liabilities	45	39	45	39	62
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	17	39	33	91
Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	76,211	78,464	76,211	78,464	77,328
Operating lease liabilities current liabilities	1,193	868	1,193	868	1,054
Operating lease liabilities noncurrent liabilities	80,043	80,120	80,043	80,120	80,559
Total operating lease liabilities	81,236	80,988	81,236	80,988	81,613
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	155,483		155,483
Regulatory Assets, Noncurrent	330,670	324,320	330,670	324,320	348,887
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	3,445		3,445
Lessee, Operating Lease, Liability, to be Paid, Year One	6,933		6,933
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,986		6,986
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,150		7,150
Lessee, Operating Lease, Liability, Payments, Due Year Four	7,185		7,185
Lessee, Operating Lease, Liability, Payments, Due after Year Five	123,784		123,784
Lessee, Operating Lease, Liability, Payments, Due	155,483		155,483
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	74,247		74,247
Total operating lease liabilities	81,236	80,988	81,236	80,988	81,613
Operating lease liabilities current liabilities	1,193	868	1,193	868	1,054
Operating lease liabilities noncurrent liabilities	80,043	80,120	80,043	80,120	80,559
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	1,717	931	3,386	2,127
Finance Lease, Principal Payments	134	302	678	457
Operating leases	0	445	154	78,433
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	$ 20	477	$ 94	710
New Headquarters Lease [Member]
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Term of Contract	20 years		20 years
Lessee, Operating Lease, Liability, Payments, Due	$ 159,400		$ 159,400
Regulatory Assets, Noncurrent	5,000	$ 2,400	5,000	$ 2,400	$ 4,200
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 159,400		$ 159,400
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	19 years		19 years