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Commitments and Contingencies - Narrative (Details) - USD ($) | 12 Months Ended
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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 |

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130551-203045 + Details
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