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Earnings Per Share Earnings Per Share (Details) - shares | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2015 | Jun. 30, 2013 | Dec. 31, 2013
Earnings Per Share [Abstract] |  |  |
stock offering | 10,400,000 | 11,100,000 | 700,000

X
- Definition Public stock offering + References No definition available. + Details
Name: | por_Stockoffering
Namespace Prefix: | por_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_EarningsPerShareAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration