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Investments in Unconsolidated Entities - White Mountain's Investments (Details) - USD ($) $ in Millions |  | 3 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
May 07, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | May 31, 2019
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Stock Issued During Period, Value, Acquisitions | $ 15.0 |  |  |  |
Ownership interest (as a percent) |  | 53.80% | 50.00% | 50.00% |
Passport/DavidShield [Member] |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Stock Issued During Period, Value, Acquisitions |  | $ 15.0 |  |  |
MediaAlpha |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 48.30% |  | 48.30% |
durchblicker |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 45.00% |  | 45.00% |
Elementum Holdings, L.P. |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 30.00% |  | 30.00% | 30.00%
JAM Partners L.P. |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  |  |  | 11.10% |
Minimum | Tuckerman Capital Funds |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 14.30% |  | 17.50% |
Minimum | Enlightenment Capital Funds |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 9.40% |  | 10.00% |
Minimum | Kudu Investments |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 3.20% |  | 3.20% |
Maximum | Tuckerman Capital Funds |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 62.30% |  | 62.40% |
Maximum | Enlightenment Capital Funds |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 36.50% |  | 38.40% |
Maximum | Kudu Investments |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Ownership interest (as a percent) |  | 35.00% |  | 30.00% |

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