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Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019
Revenue from External Customer [Line Items] |  |  |
Retention amounts included in accounts receivable | $ 9,600 | $ 6,900 |
Retained amount expected to be collected in the next twelve months | 7,400 |  |
Retained amount expected to be collected | 2,200 |  |
Research and development expenses | $ 6,670 | 6,265 | $ 6,327
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 | $ 9,600 | $ 6,900 |
Other Assets |  |  |
Revenue from External Customer [Line Items] |  |  |
Retained amount expected to be collected | $ 2,200 |  |

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