Leases - Lease Expense (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Residual Value of Leased Asset	$ 3,800	$ 3,800
Lease Expense [Abstract]
Operating Lease, Expense	1,201	2,389
Short-term Lease, Cost	$ 331	$ 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	11 years	11 years
Northwest Natural Gas Company [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 1,155	$ 2,297
Short-term Lease, Cost	331	491
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lease Expense [Abstract]
Operating Lease, Expense	46	92
Short-term Lease, Cost	$ 0	$ 0