Leases - Lease Expense - 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]
Residual Value of Leased Asset	$ 4,200	$ 3,900	$ 4,200	$ 3,900	$ 4,000
Lease Expense [Abstract]
Operating Lease, Expense	763	1,205	2,971	3,594
Short-term Lease, Cost	$ 300	323	$ 783	814
Minimum [Member]
Operating Lease Terms [Abstract]
Lessee, Operating Lease, Term of Contract	1 year		1 year
Maximum [Member]
Operating Lease Terms [Abstract]
Lessee, Operating Lease, Term of Contract	20 years		20 years
Northwest Natural Gas Company [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 746	1,158	$ 2,862	3,455
Short-term Lease, Cost	300	323	783	814
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 17	$ 47	$ 109	$ 139