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Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Oct. 31, 2020 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Dec. 31, 2018
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Reduced provision for income taxes |  | $ 8,300 |  |  |  | $ 2,200 |
Additions based on tax positions related to prior years | $ 26,400 |  | $ 4,600 |  |  |  | $ 2,700
Income tax expense (benefit) |  | 8,279 | $ 12,473 | $ 30,100 | $ 26,339 |  |
179D Deduction |  |  |  |  |  |  |
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Reduced provision for income taxes |  | 1,000 |  |  |  |  |
Tax Year 2016 |  |  |  |  |  |  |
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Income tax expense (benefit) | (6,100) |  |  |  |  |  |
Tax Year 2017 |  |  |  |  |  |  |
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Income tax expense (benefit) | (8,500) |  |  |  |  |  |
Tax Year 2018 |  |  |  |  |  |  |
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Income tax expense (benefit) | (11,900) |  |  |  |  |  |
Total Tax Years 2016-2018 |  |  |  |  |  |  |
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Income tax expense (benefit) | $ 26,500 |  |  |  |  |  |
Internal Revenue Service (IRS) |  |  |  |  |  |  |
Income Tax Examination [Line Items] |  |  |  |  |  |  |
Refund claims allowed in Income tax examination |  | $ 8,900 |  | $ 8,900 |  |  |

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