Fair Value Measurements (Narrative) (Details)	3 Months Ended
Dec. 31, 2016 USD ($)
Fair Value Disclosures [Abstract]
Transfers between measurement levels	$ 0

Amount of transfers between fair value measurement levels.

No definition available.

Name:	powl_AmountOfTransfersBetweenFairValueMeasurementLevels
Namespace Prefix:	powl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration