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Income Taxes - Additional Information (Details) - USD ($) | 3 Months Ended | 8 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2021 | Dec. 31, 2019 | Dec. 31, 2018 | Mar. 31, 2018
Income Taxes [Line Items] |  |  |  |  |
United States corporate tax at a rate |  |  | 21.00% | 34.00% |
Prior year reductions |  |  | $ 0 | $ (11,000,000) |
Accrued penalties |  |  | 0 | 0 |
Accrued interest | $ 1,800,000 |  |  |  |
Less valuation allowance |  |  | 149,200,000 | 111,900,000 |
Increase (decrease) in valuation allowance |  |  | 9,200,000 | 7,100,000 |
US branch profits, subject to tax |  |  | 0 | 0 |
Other Comprehensive Income |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Less valuation allowance |  |  | 0 | 0 |
Internal Revenue Service (IRS) |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Net operating loss carryforwards |  |  | 606,800,000 | 599,400,000 |
Operating loss carryforwards, subject to s382 limitation |  |  | 24,900,000 |  |
Operating loss carryforwards, remaining |  |  | 581,900,000 |  |
Operating loss carryforwards, subject to expiration date |  |  | 534,500,000 |  |
Operating loss carryforwards, not subject to expiration |  |  | 47,400,000 |  |
Capital loss carryforwards |  |  | 500,000 | 300,000 |
Charitable contribution carryforwards |  |  | 1,100,000 | 800,000 |
Less valuation allowance |  |  | $ 117,400,000 | 108,200,000 |
Internal Revenue Service (IRS) | Minimum |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Operating loss carryforwards, date of expiration |  |  | 2026 |  |
Internal Revenue Service (IRS) | Maximum |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Operating loss carryforwards, date of expiration |  |  | 2039 |  |
U.K. |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
U. K. corporate tax rate reduced during the period | 20.00% |  |  |  | 19.00%
Net operating loss carryforwards |  |  | $ 93,200,000 | 59,300,000 |
Capital loss carryforwards |  |  | 3,800,000 |  |
Less valuation allowance |  |  | 31,800,000 | 3,700,000 |
Increase (decrease) in valuation allowance |  |  | 28,200,000 | 0 |
U.K. | Other Comprehensive Income |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Less valuation allowance |  |  | $ 0 | 0 |
Bermuda |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Bermuda tax rate |  |  | 0.00% |  |
Forecast | U.K. |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
U. K. corporate tax rate reduced during the period |  | 17.00% |  |  |
Valuation Allowance, Operating Loss Carryforwards |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Increase (decrease) in valuation allowance |  |  | $ 9,200,000 | 7,100,000 |
Valuation Allowance, Operating Loss Carryforwards | U.K. |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Less valuation allowance |  |  | $ 28,200,000 | $ 0 |

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