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Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017
Revenue from External Customer [Line Items] |  |  |
Retention amounts included in accounts receivable | $ 5,600 | $ 4,200 |
Retention amounts expected to be collected in next fiscal year | $ 4,900 |  |
Warranty for parts and services date of shipment | 18 months |  |
Warranty parts and services date of energization | 12 months |  |
Research and development expenses | $ 6,327 | 6,717 | $ 6,906
Minimum |  |  |
Revenue from External Customer [Line Items] |  |  |
Long-term contract beginning | 1 month |  |
Accounts Receivable |  |  |
Revenue from External Customer [Line Items] |  |  |
Retention amounts included in accounts receivable | $ 5,600 | $ 4,200 |
Other Assets |  |  |
Revenue from External Customer [Line Items] |  |  |
Retention amounts expected to be collected in Fiscal 2021 | $ 700 |  |

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