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Variable Interest Entity and Noncontrolling Interests - Variable interest entity (Details) - Watford Holdings Ltd - USD ($) $ / shares in Units, $ in Millions |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Feb. 16, 2021 | Mar. 31, 2014 | Mar. 31, 2014 | Dec. 31, 2020
Variable Interest Entity [Line Items] |  |  |  |
Business acquisition, share price (per share) |  |  |  | $ 35.00
Kelso And Company |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners |  |  |  | 30.00%
Warburg Pincus |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners |  |  |  | 30.00%
Variable Interest Entity, Primary Beneficiary |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Initial capitalization amount |  |  | $ 1,100.0 |
Proceeds from from common shares issued, net |  | $ 895.6 |  |
Proceeds on issuance of preference shares |  | 219.2 |  |
Initial investment contribution amount |  | $ 100.0 |  |
Ownership percentage |  |  |  | 13.00%
Number of shares acquired |  | 2,500,000 | 2,500,000 |
Variable Interest Entity, Primary Beneficiary | Subsequent Event |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Ownership percentage | 10.30% |  |  |
Variable Interest Entity, Primary Beneficiary | Watford Merger Transaction |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Percentage ownership after merger transaction |  |  |  | 40.00%
Variable Interest Entity, Primary Beneficiary | Common shares |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Initial capitalization amount |  |  | $ 907.3 |
Variable Interest Entity, Primary Beneficiary | Preference equity |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |
Initial capitalization amount |  |  | $ 226.6 |

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