Leases - Lease Expense (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Residual Value of Leased Asset	$ 3,900	$ 3,900
Lease Expense [Abstract]
Operating Lease, Expense	1,205	3,594
Short-term Lease, Cost	$ 323	$ 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	11 years	11 years
Northwest Natural Gas Company [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 1,158	$ 3,455
Short-term Lease, Cost	323	814
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lease Expense [Abstract]
Operating Lease, Expense	47	139
Short-term Lease, Cost	$ 0	$ 0