Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2016	Jul. 22, 2016
Document Information [Line Items]
Document Type	10-Q
Document Period End Date	Jun. 30, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000073020
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Registrant Name	Northwest Natural Gas Co.
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Common Stock, Shares Outstanding		27,550,206
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q2