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Loss contingency probable loss in period.

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Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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

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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.

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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.

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

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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Commitments and Contingencies - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Guarantor Obligations [Line Items]
Rent expense	$ 3,493,000	$ 3,432,000	$ 3,734,000
Additional bonding capacity	579,500,000
Loss contingency, estimate of actual or projected loss	2,000,000
Probable liquidated damages	900,000
Failure to meet contractual commitments, reduction to revenue	800,000
Facility Agreement \| Powell (UK) Limited
Guarantor Obligations [Line Items]
Guarantee liability	5,700,000
Revolving credit facility	11,068,200
Amount of credit facility remaining borrowing capacity	5,400,000
Surety Bond
Guarantor Obligations [Line Items]
Guarantee liability	170,500,000
Canada
Guarantor Obligations [Line Items]
Rent expense	$ 700,000	$ 800,000