LONG-TERM DEBT - Narrative (Details) - USD ($)	9 Months Ended
Jun. 30, 2018	Oct. 31, 2001
U.S. Revolver
Line Of Credit Facility [Line Items]
Revolving credit facility	$ 75,000,000.0
Revolving credit facility borrowings, outstanding amount	0
Amount available under the credit facility	$ 52,700,000
Percentage of voting capital stock pledged as collateral	100.00%
Non-domestic subsidiaries of voting capital stock	65.00%
U.S. Revolver \| Maximum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	1.25%
U.S. Revolver \| Federal Funds Rate
Line Of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
U.S. Revolver \| Eurocurrency Rate
Line Of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
U.S. Revolver \| The Third Amendment
Line Of Credit Facility [Line Items]
Cash collateral percent of outstanding debt (at least)	102.00%
Cash collateral pledged balance	$ 23,600,000
U.S. Revolver \| Financial Standby Letter of Credit
Line Of Credit Facility [Line Items]
Guarantee liability	22,300,000
Industrial Development Revenue Bonds
Line Of Credit Facility [Line Items]
Borrowings		$ 8,000,000.0
Reimbursement agreement requires annual redemptions	$ 400,000
Interest rate	1.58%

Line Of Credit Facility, Collateral Amount

No definition available.

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- Definition

Line Of Credit Facility, Covenant Terms, Cash Collateral, Percent Of Debt Outstanding

+ References

No definition available.

+ Details

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- Definition

Percentage of domestic capital stock pledged as collateral for credit facility.

+ References

No definition available.

+ Details

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- Definition

Percentage of non domestic capital stock pledged as collateral for credit facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	powl_
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- Definition

Amount of the total principal payments made during the annual reporting period.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

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-Publisher FASB
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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