Leases - Lease Expense (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]
Residual Value of Leased Asset	$ 4,100	$ 3,800	$ 4,100	$ 3,800	$ 4,000
Lease Expense [Abstract]
Operating Lease, Expense	954	1,201	2,208	2,389
Short-term Lease, Cost	$ 285	331	$ 483	491
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	$ 914	1,155	$ 2,116	2,297
Short-term Lease, Cost	285	331	483	491
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 40	$ 46	$ 92	$ 92