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Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions |  | 3 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 01, 2021 | Mar. 31, 2021 | Mar. 23, 2021 | Dec. 31, 2020 | Oct. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2017 | Dec. 31, 2012 | Jul. 31, 2012
Marketing Technology (MediaAlpha) |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 28.50% |  | 35.00% |  |  |  |
Share price (in USD per share) |  | $ 35.43 |  | $ 39.07 | $ 19.00 |  |  |  |
Ark |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Investment, potential additional contribution of equity capital | $ 200.0 | $ 200.0 |  |  |  |  |  |  |
Fully diluted ownership interest after additional funding |  | 67.50% |  |  |  |  |  |  |
Ownership interest after additional funding |  | 77.10% |  |  |  |  |  |  |
Percent of shares outstanding |  | 12.50% |  |  |  |  |  |  |
Ark |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Percent of underwriting capital provided by third parties |  |  |  |  |  | 51.00% |  |  |
NSM Insurance HoldCo, LLC |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 96.60% |  |  |  |  |  |  |
Fully diluted ownership interest (as a percent) |  | 89.60% |  |  |  |  |  |  |
Asset Management (Kudu) |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 99.30% |  |  |  |  |  |  |
Fully diluted ownership interest (as a percent) |  | 84.80% |  |  |  |  |  |  |
HG Global |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  | 15.00% |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  | $ 503.0 | $ 503.0
HG Global | Preferred Stock |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 96.90% |  | 96.90% |  |  |  |  |
HG Global | Common equity securities |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 88.40% |  | 88.40% |  |  |  |  |
HG Global | Series A BAM Surplus Note |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  | $ 203.0 |  | 203.0
HG Global | Series B BAM Surplus Note |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  |  | $ 300.0
Ark |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 72.00% |  |  |  |  |  |  |
Ark | Ark |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  | 72.00% |  |  |  |  |  |  |
Fully diluted ownership interest (as a percent) |  | 63.00% |  |  |  |  |  |  |
Investment, potential additional contribution of equity capital | $ 200.0 |  |  |  |  |  |  |  |
Fully diluted ownership interest after additional funding | 67.50% |  |  |  |  |  |  |  |
Ownership interest after additional funding | 77.10% |  |  |  |  |  |  |  |
Ark | Ark |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Fully diluted ownership interest (as a percent) | 63.00% |  |  |  |  |  |  |  |
Ark | Third Point Re |  |  |  |  |  |  |  |  |
Basis of Presentation |  |  |  |  |  |  |  |  |
Reinsurance recoverable, aggregate excess loss |  | $ 50.0 |  |  |  |  |  |  |
Annual crediting rate |  | 3.00% |  |  |  |  |  |  |
Carrying value of investment |  | $ 51.7 |  |  |  |  |  |  |

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