Earnings Per Share (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Unvested performance based restricted stock	439,891	469,149	439,891	469,149

Unvested performance based restricted stock units and related dividend equivalent rights excluded from the dilutive calculation because the performance goals had not been met.

No definition available.

Name:	por_Unvestedperformancebasedrestrictedstock
Namespace Prefix:	por_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration