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Loss and Loss Adjustment Expense Reserves - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
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 | Dec. 31, 2013
Ark | Amount attributable to TPC Providers |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Percent of underwriting capital provided by third parties | 0.00% | 0.00% | 42.80% | 58.30% | 57.60% | 60.00% | 59.60% | 70.00% | 66.20% | 0.00%
Group Ark Insurance Limited |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | $ (51.7) | $ (21.5) |  |  |  |  |  |  |  |
Group Ark Insurance Limited | Property and Accident & Health |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | (20.8) | 8.9 |  |  |  |  |  |  |  |
Group Ark Insurance Limited | Specialty |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | (12.7) | 3.3 |  |  |  |  |  |  |  |
Group Ark Insurance Limited | Marine & Energy |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development | $ (18.8) |  |  |  |  |  |  |  |  |
Group Ark Insurance Limited | Casualty - Active |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development |  | 3.7 |  |  |  |  |  |  |  |
Group Ark Insurance Limited | Casualty - Runoff |  |  |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |  |  |
Favorable prior loss reserve development |  | $ 3.3 |  |  |  |  |  |  |  |

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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