Document and Entity Information	6 Months Ended
	Jun. 30, 2013	Jul. 26, 2013
Quarterly Financial Information Disclosure [Abstract]
Document Type	10-Q
Document Period End Date	Jun. 30, 2013
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		26,975,108
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2