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Fair Value Measurements (Narrative) (Details) | 12 Months Ended
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Sep. 30, 2016 USD ($)
Fair Value Disclosures [Abstract] |
Transfers between measurement levels | $ 0

X
- Definition Amount of transfers between fair value measurement levels. + References No definition available. + Details
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Namespace Prefix: | powl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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