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Loss and Loss Adjustment Expense Reserves - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Ark |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | $ 19.9 | $ (51.7) | $ (21.5) |  |  |  |  |  |  |
Syndicate - Ark Insurance Holdings Limited |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Percent of underwriting capital provided by third parties | 0.00% | 0.00% | 0.00% | 42.80% | 58.30% | 57.60% | 60.00% | 59.60% | 70.00% | 66.20%
Property and Accident & Health | Ark |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | $ 41.7 | $ (20.8) | $ 8.9 |  |  |  |  |  |  |
Specialty | Ark |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | (11.9) | (12.7) | 3.3 |  |  |  |  |  |  |
Casualty-Runoff | Ark |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | $ (6.0) |  | 3.3 |  |  |  |  |  |  |
Marine & Energy | Ark |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development |  | $ (18.8) |  |  |  |  |  |  |  |
Casualty-Active | Ark |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development |  |  | $ 3.7 |  |  |  |  |  |  |

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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