Subsequent Event (details)	6 Months Ended
	Jun. 30, 2012
Subsequent Events Level 4 [Abstract]
Subsequent Event, Description	On July 12, 2012, NW Natural entered into a bond purchase agreement under which a group of investors agreed to purchase $50 million of our first mortgage bonds with a coupon rate of 4.00 percent and a 30 year maturity. The bond issuance is subject to customary closing conditions and is expected to close on or before October 31, 2012. The proceeds of the issuance are to be used to reduce short-term debt and for other general corporate purposes.