Investment Securities - Fair Value Measurement by Level (Details) - USD ($)
$ in Millions |
Mar. 31, 2025 |
Dec. 31, 2024 |
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
$ 541.8
|
$ 650.0
|
| Other long-term investments |
2,287.9
|
2,150.2
|
| U.S. Government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
490.9
|
462.1
|
| Debt securities issued by corporations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
1,398.5
|
1,414.2
|
| Municipal obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
3.2
|
3.2
|
| Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
379.9
|
373.9
|
| Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
256.0
|
236.7
|
| Foreign government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
23.5
|
21.5
|
| Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
2,552.0
|
2,511.6
|
| Level 2 | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
379.9
|
373.9
|
| Level 2 | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
256.0
|
236.7
|
| Level 3 | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Level 3 | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fair value investments |
6,551.3
|
6,477.6
|
| Fair value measured on a recurring basis | MediaAlpha |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
165.0
|
201.6
|
| Fair value measured on a recurring basis | U.S. Government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
490.9
|
462.1
|
| Fair value measured on a recurring basis | Debt securities issued by corporations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
1,398.5
|
1,414.2
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Financials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
474.4
|
466.7
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
263.1
|
255.2
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
150.2
|
164.4
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Healthcare |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
144.2
|
153.1
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Technology |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
119.3
|
113.8
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Communications |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
64.5
|
71.6
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Materials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
63.8
|
65.7
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
60.7
|
60.9
|
| Fair value measured on a recurring basis | Debt securities issued by corporations | Energy |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
58.3
|
62.8
|
| Fair value measured on a recurring basis | Municipal obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
3.2
|
3.2
|
| Fair value measured on a recurring basis | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
379.9
|
373.9
|
| Fair value measured on a recurring basis | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
256.0
|
236.7
|
| Fair value measured on a recurring basis | Foreign government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
23.5
|
21.5
|
| Fair value measured on a recurring basis | Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
2,552.0
|
2,511.6
|
| Fair value measured on a recurring basis | Short-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Short-term investments, at fair value |
1,004.6
|
964.2
|
| Fair value measured on a recurring basis | Exchange-traded funds |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
120.9
|
224.6
|
| Fair value measured on a recurring basis | Common stock, other |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
420.9
|
425.4
|
| Fair value measured on a recurring basis | Common equity securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
541.8
|
650.0
|
| Fair value measured on a recurring basis | Other Long-Term Investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
2,287.9
|
2,150.2
|
| Fair value measured on a recurring basis | Fair Value, Inputs, Level 1, Level 2, and Level 3 | Other long-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
1,401.4
|
1,286.2
|
| Fair value measured on a recurring basis | Level 1 |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fair value investments |
1,777.0
|
1,838.6
|
| Fair value measured on a recurring basis | Level 1 | MediaAlpha |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
165.0
|
201.6
|
| Fair value measured on a recurring basis | Level 1 | U.S. Government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
490.1
|
461.3
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Financials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Consumer |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Industrial |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Healthcare |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Technology |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Communications |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Materials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Utilities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations | Energy |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Municipal obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Foreign government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
490.1
|
461.3
|
| Fair value measured on a recurring basis | Level 1 | Short-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Short-term investments, at fair value |
1,001.0
|
951.1
|
| Fair value measured on a recurring basis | Level 1 | Exchange-traded funds |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
120.9
|
224.6
|
| Fair value measured on a recurring basis | Level 1 | Common stock, other |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Common equity securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
120.9
|
224.6
|
| Fair value measured on a recurring basis | Level 1 | Other long-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 1 | Other Long-Term Investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 2 |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fair value investments |
2,511.9
|
2,512.3
|
| Fair value measured on a recurring basis | Level 2 | MediaAlpha |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 2 | U.S. Government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.8
|
0.8
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
1,398.5
|
1,414.2
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Financials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
474.4
|
466.7
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Consumer |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
263.1
|
255.2
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Industrial |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
150.2
|
164.4
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Healthcare |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
144.2
|
153.1
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Technology |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
119.3
|
113.8
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Communications |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
64.5
|
71.6
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Materials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
63.8
|
65.7
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Utilities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
60.7
|
60.9
|
| Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations | Energy |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
58.3
|
62.8
|
| Fair value measured on a recurring basis | Level 2 | Municipal obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
3.2
|
3.2
|
| Fair value measured on a recurring basis | Level 2 | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
379.9
|
373.9
|
| Fair value measured on a recurring basis | Level 2 | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
256.0
|
236.7
|
| Fair value measured on a recurring basis | Level 2 | Foreign government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
23.5
|
21.5
|
| Fair value measured on a recurring basis | Level 2 | Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
2,061.9
|
2,050.3
|
| Fair value measured on a recurring basis | Level 2 | Short-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Short-term investments, at fair value |
3.6
|
13.1
|
| Fair value measured on a recurring basis | Level 2 | Exchange-traded funds |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 2 | Common stock, other |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
420.9
|
425.4
|
| Fair value measured on a recurring basis | Level 2 | Common equity securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
420.9
|
425.4
|
| Fair value measured on a recurring basis | Level 2 | Other long-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
25.5
|
23.5
|
| Fair value measured on a recurring basis | Level 2 | Other Long-Term Investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
25.5
|
23.5
|
| Fair value measured on a recurring basis | Level 3 |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fair value investments |
1,375.9
|
1,262.7
|
| Fair value measured on a recurring basis | Level 3 | MediaAlpha |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | U.S. Government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Financials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Consumer |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Industrial |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Healthcare |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Technology |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Communications |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Materials |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Utilities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations | Energy |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Municipal obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Foreign government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Short-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Short-term investments, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Exchange-traded funds |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Common stock, other |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Common equity securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
0.0
|
0.0
|
| Fair value measured on a recurring basis | Level 3 | Other long-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
1,375.9
|
1,262.7
|
| Fair value measured on a recurring basis | Level 3 | Other Long-Term Investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
1,375.9
|
1,262.7
|
| Fair value measured on a recurring basis | NAV | Other long-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
$ 886.5
|
$ 864.0
|