Leases - Lease Asset and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Finance Lease, Liability, Payments, Due Next Twelve Months	$ 400		$ 400
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	78,566	$ 5,013	78,566	$ 5,013	$ 2,950
Operating lease liabilities current liabilities	931	4,271	931	4,271	2,101
Operating lease liabilities noncurrent liabilities	80,159	721	80,159	721	841
Total operating lease liabilities	$ 81,090	$ 4,992	$ 81,090	$ 4,992	$ 2,942
Operating Lease, Weighted Average Remaining Lease Term	19 years 8 months 12 days	1 year 1 month 6 days	19 years 8 months 12 days	1 year 1 month 6 days	1 year
Operating Lease, Weighted Average Discount Rate, Percent	7.24%	3.82%	7.24%	3.82%	3.98%
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 2,376		$ 2,376
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,813		6,813
Lessee, Operating Lease, Liability, Payments, Due Year Three	6,866		6,866
Lessee, Operating Lease, Liability, Payments, Due Year Four	6,983		6,983
Lessee, Operating Lease, Liability, Payments, Due Year Five	7,146		7,146
Lessee, Operating Lease, Liability, Payments, Due after Year Five	130,912		130,912
Lessee, Operating Lease, Liability, Payments, Due	161,096		161,096
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	80,006		80,006
Total operating lease liabilities	81,090	$ 4,992	81,090	$ 4,992	$ 2,942
Operating lease liabilities current liabilities	931	4,271	931	4,271	2,101
Operating lease liabilities noncurrent liabilities	80,159	721	80,159	721	841
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	161,096		161,096
Regulatory Assets, Noncurrent	324,358	318,340	324,358	318,340	343,146
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	970	1,159	2,218	2,293
Finance Lease, Principal Payments	302	0	457	0
Operating leases	445	0	78,433	7,291
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	477	0	710	0
Finance Leases [Abstract]
Finance Lease, Right-of-Use Asset	1,100	300	1,100	300	500
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	102	216	102	216	190
Operating lease liabilities current liabilities	63	130	63	130	122
Operating lease liabilities noncurrent liabilities	39	87	39	87	69
Total operating lease liabilities	102	217	102	217	191
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	35		35
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	105		105
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	3		3
Total operating lease liabilities	102	217	102	217	191
Operating lease liabilities current liabilities	63	130	63	130	122
Operating lease liabilities noncurrent liabilities	39	87	39	87	69
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	105		105
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	39	44	91	87
Operating leases	0	0	0	304
Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating lease right of use asset	78,464	4,797	78,464	4,797	2,760
Operating lease liabilities current liabilities	868	4,141	868	4,141	1,979
Operating lease liabilities noncurrent liabilities	80,120	634	80,120	634	772
Total operating lease liabilities	80,988	4,775	80,988	4,775	2,751
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	2,341		2,341
Lessee, Operating Lease, Liability, Payments, Due Year Two	6,761		6,761
Lessee, Operating Lease, Liability, Payments, Due Year Three	6,848		6,848
Lessee, Operating Lease, Liability, Payments, Due Year Four	6,983		6,983
Lessee, Operating Lease, Liability, Payments, Due Year Five	7,146		7,146
Lessee, Operating Lease, Liability, Payments, Due after Year Five	130,912		130,912
Lessee, Operating Lease, Liability, Payments, Due	160,991		160,991
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	80,003		80,003
Total operating lease liabilities	80,988	4,775	80,988	4,775	2,751
Operating lease liabilities current liabilities	868	4,141	868	4,141	1,979
Operating lease liabilities noncurrent liabilities	80,120	634	80,120	634	772
Commencement of Significant Lease [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	160,991		160,991
Regulatory Assets, Noncurrent	324,320	318,340	324,320	318,340	$ 343,146
Leases Cash Flow [Abstract]
Operating cash flows from operating leases	931	1,115	2,127	2,206
Finance Lease, Principal Payments	302	0	457	0
Operating leases	445	0	78,433	6,987
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	477	$ 0	710	$ 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	$ 2,400		$ 2,400
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