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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Income Tax [Line Items] |  |  |  |  |
Effective income tax expense (benefit) rate | 17.50% | 5.00% | 26.90% | 11.20% |
Alternative minimum tax credit carry forward |  |  |  |  | $ 11.0
Net operating loss carryforwards | $ 24.9 |  | $ 24.9 |  | 21.9
Section 163(j) carryforward | 6.8 |  | 6.8 |  | $ 9.0
Alternative Minimum Tax Credits |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Income tax refunds received | $ 5.5 |  | $ 11.0 |  |
UNITED STATES |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates | 21.00% |  | 21.00% |  |
BERMUDA |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates | 0.00% |  | 0.00% |  |
CAYMAN ISLANDS |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates |  |  | 0.00% |  |
UNITED KINGDOM |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates |  |  | 19.00% |  |
IRELAND | Non Trading Income |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates |  |  | 25.00% |  |
IRELAND | Capital Gain |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates |  |  | 33.00% |  |
IRELAND | Trading Income |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Statutory income tax rates |  |  | 12.50% |  |

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