Derivative Instruments Credit Rating (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Derivative [Line Items]
Unrealized losses on derivatives	$ 500,000
Collateral Posted with NW Natural Counterparties [Member]
Derivative [Line Items]
Additional Collateral, Aggregate Fair Value	0.0	$ 0.0
Northwest Natural Gas Company [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	6,400,000	3,600,000	$ 2,200,000
Derivative liability	2,000,000	$ 9,300,000	$ 19,900,000
Northwest Natural Gas Company [Member] | (Current Ratings) A/A3
Derivative [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Northwest Natural Gas Company [Member] | BBB/Baa1
Derivative [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Northwest Natural Gas Company [Member] | BBB/Baa2
Derivative [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Northwest Natural Gas Company [Member] | BBB-/Baa3
Derivative [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Northwest Natural Gas Company [Member] | Speculative
Derivative [Line Items]
With Adequate Assurance Calls	604,000
Without Adequate Assurance Calls	$ 185,000