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Income Taxes - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017
Income Taxes [Line Items] |  |  |  |  |
United States statutory tax rate | 35.00% | 21.00% | 21.00% |  |
Cash and cash equivalents held by foreign subsidiaries |  | $ 5,800 |  |  |
Temporary difference related to undistributed earnings |  | 11,600 | $ 12,900 |  |
Unrecognized tax liabilities |  | 0 | 0 |  |
Valuation allowance against net deferred tax assets |  | 4,882 | 964 |  |
United States |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Net operating loss, carryforwards |  | 51,000 |  |  | $ 28,300
Net operating loss, carryforwards expiration year |  |  |  |  | 2028
Tax Cuts And Jobs Act Of 2017, change in tax rate income tax expense benefit |  |  |  | $ 22,700 |
Valuation allowance against net deferred tax assets |  | 25,700 | 20,800 |  |
Canada |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Net operating loss, carryforwards |  | $ 16,800 |  |  |
Net operating loss, carryforwards expiration year |  | 2033 |  |  |
Valuation allowance against net deferred tax assets |  | $ 5,600 | $ 5,300 |  |
Russia |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Net operating loss, carryforwards |  | $ 1,100 |  |  |
Net operating loss, carryforwards expiration year |  | 2026 |  |  |
Valuation allowance against net deferred tax assets |  | $ 200 |  |  |

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