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Investment Securities - Fair Value Measurement by Level (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Investment securities |  |  |
Other long-term investments | $ 1,377.8 | $ 786.8 |
Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 992.9 | 547.4 |
Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 277.6 | 218.5 |
Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 135.0 | 0.0 |
Level 2 | Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 277.6 | 218.5 |
Level 2 | Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 135.0 | 0.0 |
Level 3 |  |  |
Investment securities |  |  |
Other long-term investments | 890.6 |  |
Level 3 | Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Level 3 | Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Level 3 | Common equity securities |  |  |
Investment securities |  |  |
Fair value investments |  | 0.0 | $ 0.1
Level 3 | Other long-term investments |  |  |
Investment securities |  |  |
Fair value investments | 890.6 | 614.2 | $ 654.0
Fair value measured on a recurring basis |  |  |
Investment securities |  |  |
Fair value investments | 4,265.3 | 2,939.0 |
Other long-term investments | 1,377.8 | 786.8 |
Fair value measured on a recurring basis | MediaAlpha |  |  |
Investment securities |  |  |
Other long-term investments | 261.6 | 802.2 |
Fair value measured on a recurring basis | U.S. Government and agency obligations |  |  |
Investment securities |  |  |
Fair value investments | 211.5 | 176.3 |
Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 992.9 | 547.4 |
Fair value measured on a recurring basis | Municipal obligations |  |  |
Investment securities |  |  |
Fair value investments | 291.9 | 265.0 |
Fair value measured on a recurring basis | Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 277.6 | 218.5 |
Fair value measured on a recurring basis | Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 135.0 |  |
Fair value measured on a recurring basis | Fixed maturity investments |  |  |
Investment securities |  |  |
Fair value investments | 1,908.9 | 1,207.2 |
Fair value measured on a recurring basis | Short-term investments |  |  |
Investment securities |  |  |
Short-term investments, at fair value | 465.9 | 142.8 |
Fair value measured on a recurring basis | Common equity securities |  |  |
Investment securities |  |  |
Fair value investments | 251.1 |  |
Fair value measured on a recurring basis | Other long-term investments |  |  |
Investment securities |  |  |
Fair value investments | 895.3 | 614.2 |
Fair value measured on a recurring basis | Other long-term investments — NAV |  |  |
Investment securities |  |  |
Fair value investments | 482.5 | 172.6 |
Fair value measured on a recurring basis | Level 1 |  |  |
Investment securities |  |  |
Fair value investments | 939.0 | 1,121.3 |
Other long-term investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 1 | MediaAlpha |  |  |
Investment securities |  |  |
Other long-term investments | 261.6 | 802.2 |
Fair value measured on a recurring basis | Level 1 | U.S. Government and agency obligations |  |  |
Investment securities |  |  |
Fair value investments | 211.5 | 176.3 |
Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 1 | Municipal obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 1 | Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 1 | Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Fair value measured on a recurring basis | Level 1 | Fixed maturity investments |  |  |
Investment securities |  |  |
Fair value investments | 211.5 | 176.3 |
Fair value measured on a recurring basis | Level 1 | Short-term investments |  |  |
Investment securities |  |  |
Short-term investments, at fair value | 465.9 | 142.8 |
Fair value measured on a recurring basis | Level 1 | Common equity securities |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Fair value measured on a recurring basis | Level 1 | Other long-term investments |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 1 | Other long-term investments — NAV |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 2 |  |  |
Investment securities |  |  |
Fair value investments | 1,953.2 | 1,030.9 |
Other long-term investments | 4.7 | 0.0 |
Fair value measured on a recurring basis | Level 2 | MediaAlpha |  |  |
Investment securities |  |  |
Other long-term investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 2 | U.S. Government and agency obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 992.9 | 547.4 |
Fair value measured on a recurring basis | Level 2 | Municipal obligations |  |  |
Investment securities |  |  |
Fair value investments | 291.9 | 265.0 |
Fair value measured on a recurring basis | Level 2 | Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 277.6 | 218.5 |
Fair value measured on a recurring basis | Level 2 | Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 135.0 |  |
Fair value measured on a recurring basis | Level 2 | Fixed maturity investments |  |  |
Investment securities |  |  |
Fair value investments | 1,697.4 | 1,030.9 |
Fair value measured on a recurring basis | Level 2 | Short-term investments |  |  |
Investment securities |  |  |
Short-term investments, at fair value | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 2 | Common equity securities |  |  |
Investment securities |  |  |
Fair value investments | 251.1 |  |
Fair value measured on a recurring basis | Level 2 | Other long-term investments |  |  |
Investment securities |  |  |
Fair value investments | 4.7 | 0.0 |
Fair value measured on a recurring basis | Level 2 | Other long-term investments — NAV |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 |  |  |
Investment securities |  |  |
Fair value investments | 890.6 | 614.2 |
Other long-term investments | 890.6 | 614.2 |
Fair value measured on a recurring basis | Level 3 | MediaAlpha |  |  |
Investment securities |  |  |
Other long-term investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | U.S. Government and agency obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | Municipal obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | Mortgage and asset-backed securities |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | Collateralized loan obligations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Fair value measured on a recurring basis | Level 3 | Fixed maturity investments |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | Short-term investments |  |  |
Investment securities |  |  |
Short-term investments, at fair value | 0.0 | 0.0 |
Fair value measured on a recurring basis | Level 3 | Common equity securities |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Fair value measured on a recurring basis | Level 3 | Other long-term investments |  |  |
Investment securities |  |  |
Fair value investments | 890.6 | 614.2 |
Fair value measured on a recurring basis | Level 3 | Other long-term investments — NAV |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Financials | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 264.2 | 133.9 |
Financials | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Financials | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 264.2 | 133.9 |
Financials | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Consumer | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 178.1 | 81.9 |
Consumer | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Consumer | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 178.1 | 81.9 |
Consumer | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Technology | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 117.9 | 66.7 |
Technology | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Technology | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 117.9 | 66.7 |
Technology | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Industrial | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 112.9 | 66.9 |
Industrial | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Industrial | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 112.9 | 66.9 |
Industrial | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Healthcare | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 112.8 | 51.5 |
Healthcare | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Healthcare | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 112.8 | 51.5 |
Healthcare | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Utilities | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 70.9 | 32.3 |
Utilities | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Utilities | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 70.9 | 32.3 |
Utilities | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Communications | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 56.0 | 44.5 |
Communications | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Communications | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 56.0 | 44.5 |
Communications | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Energy | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 48.0 | 35.8 |
Energy | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Energy | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 48.0 | 35.8 |
Energy | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Materials | Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 32.1 | 33.9 |
Materials | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 0.0 |
Materials | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 32.1 | 33.9 |
Materials | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | $ 0.0 | $ 0.0 |

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