Leases - Lease Expense (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Residual Value of Leased Asset	$ 0
Lease Expense [Abstract]
Operating Lease, Expense	1,188,000
Short-term Lease, Cost	$ 160,000
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	11 years
Northwest Natural Gas Company [Member]
Lease Expense [Abstract]
Operating Lease, Expense	$ 1,142,000
Short-term Lease, Cost	160,000
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lease Expense [Abstract]
Operating Lease, Expense	46,000
Short-term Lease, Cost	$ 0