Subsequent Event (details)	9 Months Ended
	Sep. 30, 2012
Subsequent Events Level 4 [Abstract]
Subsequent Event, Description	In October 2012, the OPUC authorized an annual Oregon revenue increase of $8.7 million, equivalent to a rate increase of 1.2 percent, effective November 1, 2012. This annual increase included an authorized return on equity of 9.5 percent and an overall rate of return on rate base of 7.78 percent at a 50 percent equity and 50 percent long-term debt capital structure. This increase includes the recovery of amounts that had previously been deferred through the company's decoupling mechanism of about $15 million. As a result, the overall effect on the Company is a decline in net operating revenues (utility margin) of approximately $6 million on an annualized basis. In addition to our decoupling mechanism, the OPUC also approved the retention of our current weather normalization mechanism. Our system integrity program was extended for two years. They also authorized a SRRM that allows the Company to recover prudently incurred environmental site remediation costs. The OPUC denied recovery of deferred amounts that represent the increase in deferred income taxes caused by the 2009 Oregon tax rate change, resulting in a one-time, after-tax charge of $2.7 million in the third quarter of 2012. The OPUC deferred various items for future resolution in separate proceedings including the Commission's review of the Company's recovery of its working gas inventory carrying costs, the decision regarding whether prepaid pension asset should be included in rate base, and the Commission's review of the Company's revenue-sharing arrangement on its interstate storage activities. In July 2012, we signed a bond purchase agreement with investors which closed on October 30, 2012, whereby we issued $50 million of NW Natural first mortgage bonds with a coupon rate of 4.00 percent and a 30-year maturity. The proceeds of the issuance will be used to reduce short-term debt and for other general corporate purposes.