Leases - Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Residual Value of Leased Asset	$ 4,100		$ 4,000
Lease Expense [Abstract]
Operating Lease, Expense	1,254	$ 1,188
Short-term Lease, Cost	$ 198	160
Minimum [Member]
Operating Lease Terms [Abstract]
Lessee, Operating Lease, Term of Contract	1 year
Maximum [Member]
Operating Lease Terms [Abstract]
Lessee, Operating Lease, Term of Contract	20 years
Northwest Natural Gas Company [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 1,202	1,142
Short-term Lease, Cost	198	160
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lease Expense [Abstract]
Operating Lease, Expense	52	46
Short-term Lease, Cost	$ 0	$ 0