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Income Taxes - Additional Information (Details) - USD ($) | 3 Months Ended | 8 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2017 | Mar. 31, 2021 | Dec. 31, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2020
Income Taxes [Line Items] |  |  |  |  |  |  |  |
United States corporate tax at a rate |  |  |  |  | 34.00% |  |  |
Foreign exchange |  |  |  |  | $ (2,100,000) | $ 200,000 | $ (400,000) |
Prior year adjustments |  |  |  |  | 1,300,000 | 3,300,000 | (4,500,000) |
Income tax examination, interest accrued |  |  |  |  | 400,000 | 1,300,000 |  |
Income tax examination, cumulative interest accrued |  |  |  |  | 1,700,000 | 1,300,000 |  |
Impact of unrecognized tax benefits |  |  |  |  | 100,000 | (1,900,000) | 0 |
Effective Income Rate Tax Reconciliation, Tax Settlement, Foreign Credit, Amount |  |  |  |  | 300,000 | 3,200,000 |  |
Unrecognized tax benefits |  |  |  |  | 11,200,000 | 10,500,000 | $ 29,200,000 |
Foreign exchange re-translation |  |  |  |  | 1,000,000 | 3,400,000 |  |
Settlement in respect of tax position of prior years |  |  |  |  | (300,000) | (15,300,000) |  |
Accrued interest and penalties |  |  |  |  | 0 | 0 |  |
Less valuation allowance |  |  |  |  | (104,800,000) | (142,500,000) |  |
Increase (decrease) in valuation allowance |  |  |  |  | 38,400,000 | (20,700,000) |  |
Foreign tax credit carryforwards |  |  |  |  | 4,000,000 | 2,500,000 |  |
US branch profits, subject to tax |  |  |  |  | 0 | 1,900,000 |  |
Other Comprehensive Income |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Less valuation allowance |  |  |  |  | 0 | (300,000) |  |
Internal Revenue Service (IRS) |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Net operating loss carryforwards |  |  |  |  | 482,700,000 | 343,200,000 |  |
Capital loss carryforwards |  |  |  |  | 500,000 | 500,000 |  |
Charitable contribution carryforwards |  |  |  |  | 700,000 | 500,000 |  |
Less valuation allowance |  |  |  |  | $ (101,100,000) | (139,200,000) |  |
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 |  |  |  |  | 2036 |  |  |
U.K. |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
U. K. corporate tax rate reduced during the period | 20.00% |  |  |  |  |  |  |
Net operating loss carryforwards |  |  |  |  | $ 84,900,000 | 18,200,000 |  |
Capital loss carryforwards |  |  |  |  | 3,800,000 |  |  |
Less valuation allowance |  |  |  |  | (3,700,000) | (3,300,000) |  |
Increase (decrease) in valuation allowance |  |  |  |  | (400,000) | (2,600,000) |  |
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 |  |  |  |  | $ 38,400,000 | (21,000,000) |  |
Valuation Allowance, Operating Loss Carryforwards | U.K. |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
Less valuation allowance |  |  |  |  | $ (400,000) | $ (2,700,000) |  |
Subsequent Event |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
United States corporate tax at a rate |  |  | 21.00% |  |  |  |  |
Foreign tax credit carryforwards |  |  |  |  |  |  |  | $ 1,200,000
Subsequent Event | U.K. |  |  |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |  |  |
U. K. corporate tax rate reduced during the period |  |  |  | 19.00% |  |  |  |

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