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Stock-Based Compensation (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
6 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Feb. 28, 2015
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 161,337us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
    106,845us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Compensation expense $ 0.9us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
$ 1.5us-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 $ 0.7us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
$ 0.5us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
   
Restricted Stock | 2014 Non-Employee Director Equity Incentive Plan        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting period     2 years  
Shares issued under the plan     16,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= powl_NonEmployeeDirectorEquityIncentivePlanMember
 
Shares issued, price per share     $ 33.37us-gaap_SharesIssuedPricePerShare
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= powl_NonEmployeeDirectorEquityIncentivePlanMember
 
Restricted Stock | 2014 Non-Employee Director Equity Incentive Plan | Vesting of First Anniversary        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting percentage     50.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= powl_NonEmployeeDirectorEquityIncentivePlanMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheOneMember
 
Restricted Stock | 2014 Non-Employee Director Equity Incentive Plan | Vesting of Second Anniversary        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Vesting percentage     50.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= powl_NonEmployeeDirectorEquityIncentivePlanMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheTwoMember
 
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