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Stock-Based Compensation (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Sep. 30, 2014
Restricted Stock Units (RSUs)      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Vesting period 3 years    
Unvested restricted stock outstanding 167,137us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
  106,845us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Compensation expense $ 0.8us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
$ 0.9us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
 
Restricted Stock Units (RSUs) | Performance Based Restricted Stock Unit      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Vesting period 3 years    
Actual amount of RSUs earned based on cumulative earnings 60.00%powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentOfActualAmountOfUnitsEarned
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_StatementClassOfStockAxis
= powl_PerformanceBasedRestrictedStockUnitMember
   
Restricted Stock Units (RSUs) | Time Based Restricted Stock Unit      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Vesting period 3 years    
Target RSUs granted range 40.00%powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetRSUGrantedRange
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_StatementClassOfStockAxis
= powl_TimeBasedRestrictedStockUnitMember
   
Restricted Stock      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Compensation expense $ 0.3us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
$ 0.2us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
 
Minimum | Restricted Stock Units (RSUs) | Performance Based Restricted Stock Unit      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Target RSUs granted range 0.00%powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetRSUGrantedRange
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementClassOfStockAxis
= powl_PerformanceBasedRestrictedStockUnitMember
   
Maximum | Restricted Stock Units (RSUs) | Performance Based Restricted Stock Unit      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Target RSUs granted range 150.00%powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetRSUGrantedRange
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementClassOfStockAxis
= powl_PerformanceBasedRestrictedStockUnitMember