Leases - Lease Asset and Liabilities - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Finance Lease, Liability, Payments, Due Next Twelve Months	$ 900		$ 900
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	78,036	$ 3,917	78,036	$ 3,917	$ 2,950
Operating lease liabilities current liabilities	1,081	3,171	1,081	3,171	2,101
Operating lease liabilities noncurrent liabilities	80,854	732	80,854	732	841
Total operating lease liabilities	$ 81,935	$ 3,903	$ 81,935	$ 3,903	$ 2,942
Operating Lease, Weighted Average Remaining Lease Term	19 years 4 months 24 days	10 months 24 days	19 years 4 months 24 days	10 months 24 days	1 year
Operating Lease, Weighted Average Discount Rate, Percent	7.22%	3.86%	7.22%	3.86%	3.98%
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 1,682		$ 1,682
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,813		6,813
Lessee, Operating Lease, Liability, Payments, Due Year Three	6,867		6,867
Lessee, Operating Lease, Liability, Payments, Due Year Four	6,986		6,986
Lessee, Operating Lease, Liability, Payments, Due Year Five	7,150		7,150
Lessee, Operating Lease, Liability, Payments, Due after Year Five	130,969		130,969
Lessee, Operating Lease, Liability, Payments, Due	160,467		160,467
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	78,532		78,532
Total operating lease liabilities	81,935	$ 3,903	81,935	$ 3,903	$ 2,942
Operating lease liabilities current liabilities	1,081	3,171	1,081	3,171	2,101
Operating lease liabilities noncurrent liabilities	80,854	732	80,854	732	841
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	160,467		160,467
Regulatory Assets, Noncurrent	324,176	313,890	324,176	313,890	343,146
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	691	1,158	2,909	3,451
Finance Lease, Principal Payments	215	0	672	0
Operating leases	106	0	78,539	7,358
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	676	0	1,386	0
Finance Leases [Abstract]
Finance Lease, Right-of-Use Asset	1,800	300	1,800	300	500
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	87	172	87	172	190
Operating lease liabilities current liabilities	61	96	61	96	122
Operating lease liabilities noncurrent liabilities	24	78	24	78	69
Total operating lease liabilities	85	174	85	174	191
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	17		17
Lessee, Operating Lease, Liability, Payments, Due Year Two	52		52
Lessee, Operating Lease, Liability, Payments, Due Year Three	18		18
Lessee, Operating Lease, Liability, Payments, Due Year Four	0		0
Lessee, Operating Lease, Liability, Payments, Due Year Five	0		0
Lessee, Operating Lease, Liability, Payments, Due after Year Five	0		0
Lessee, Operating Lease, Liability, Payments, Due	87		87
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	2		2
Total operating lease liabilities	85	174	85	174	191
Operating lease liabilities current liabilities	61	96	61	96	122
Operating lease liabilities noncurrent liabilities	24	78	24	78	69
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	87		87
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	18	45	109	132
Operating leases	0	0	0	304
Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	77,949	3,745	77,949	3,745	2,760
Operating lease liabilities current liabilities	1,020	3,075	1,020	3,075	1,979
Operating lease liabilities noncurrent liabilities	80,830	654	80,830	654	772
Total operating lease liabilities	81,850	3,729	81,850	3,729	2,751
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	1,665		1,665
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,761		6,761
Lessee, Operating Lease, Liability, Payments, Due Year Three	6,849		6,849
Lessee, Operating Lease, Liability, Payments, Due Year Four	6,986		6,986
Lessee, Operating Lease, Liability, Payments, Due Year Five	7,150		7,150
Lessee, Operating Lease, Liability, Payments, Due after Year Five	130,969		130,969
Lessee, Operating Lease, Liability, Payments, Due	160,380		160,380
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	78,530		78,530
Total operating lease liabilities	81,850	3,729	81,850	3,729	2,751
Operating lease liabilities current liabilities	1,020	3,075	1,020	3,075	1,979
Operating lease liabilities noncurrent liabilities	80,830	654	80,830	654	772
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	160,380		160,380
Regulatory Assets, Noncurrent	324,136	313,890	324,136	313,890	$ 343,146
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	673	1,113	2,800	3,319
Finance Lease, Principal Payments	215	0	672	0
Operating leases	106	0	78,539	7,054
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	676	$ 0	1,386	$ 0
New Headquarters Lease [Member]
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 159,400		$ 159,400
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	20 years		20 years
Lessee, Operating Lease, Liability, Payments, Due	$ 159,400		$ 159,400
Regulatory Assets, Noncurrent	$ 3,700		$ 3,700
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		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		7 years