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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

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- Definition Unvested performance based restricted stock units and related dividend equivalent rights excluded from the dilutive calculation because the performance goals had not been met. + References No definition available. + Details
Name: | por_Unvestedperformancebasedrestrictedstock
Namespace Prefix: | por_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_EarningsPerShareAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration