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Third Party Reinsurance - Schedule of Reinsurance (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Earned premiums: |  |  |  |
Gross earned premiums | $ 124.3 | $ 5.6 | $ 235.3 | $ 11.0
Losses and Loss Adjustment Expense [Abstract] |  |  |  |
Reinsurance recoverables on unpaid losses | 425.3 |  | 425.3 |
Reinsurance recoverables on paid losses | $ 6.0 |  | $ 6.0 |
Percent of reinsurance recoverables from insurers with excellent or higher credit quality | 87.60% |  | 87.60% |
Percent of reinsurance recoverables from insurers that are collateralized | 7.50% |  | 7.50% |
Ark |  |  |  |
Written premiums: |  |  |  |
Gross | $ 328.1 |  | $ 732.6 |
Ceded | (65.9) |  | (128.0) |
Gross written premiums | 262.2 |  | 604.6 |
Earned premiums: |  |  |  |
Gross | 174.9 |  | 337.5 |
Ceded | (57.1) |  | (115.1) |
Gross earned premiums | 117.8 |  | 222.4 |
Losses and Loss Adjustment Expense [Abstract] |  |  |  |
Gross | 63.6 |  | 179.2 |
Ceded | (11.0) |  | (60.6) |
Net Losses and LAE | 52.6 |  | 118.6 |
Amount attributable to TPC Providers |  |  |  |
Losses and Loss Adjustment Expense [Abstract] |  |  |  |
Reinsurance recoverables on unpaid losses | 314.6 |  | 314.6 |
All Entities Except TCP Providers |  |  |  |
Losses and Loss Adjustment Expense [Abstract] |  |  |  |
Reinsurance recoverables on unpaid losses | $ 110.7 |  | $ 110.7 |

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