Investment Securities - Fair Value Measurement by Level (Details) - USD ($)
$ in Millions |
Mar. 31, 2026 |
Dec. 31, 2025 |
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
$ 546.5
|
$ 483.0
|
| Other long-term investments |
3,253.5
|
2,958.5
|
| U.S. Government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
477.7
|
460.3
|
| Debt securities issued by corporations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
1,628.8
|
1,537.7
|
| Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
402.5
|
393.0
|
| Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
345.2
|
347.0
|
| Foreign government and agency obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
31.9
|
32.5
|
| Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
2,886.1
|
2,770.5
|
| Level 2 | Mortgage and asset-backed securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
402.5
|
393.0
|
| Level 2 | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
345.2
|
347.0
|
| Level 3 | Recent transaction |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
125.4
|
250.4
|
| 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] |
|
|
| Total investments |
8,354.0
|
8,324.9
|
| Fair value measured on a recurring basis | MediaAlpha |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
166.1
|
231.2
|
| 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 |
477.7
|
460.3
|
| 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 |
1,628.8
|
1,537.7
|
| 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 |
589.4
|
531.5
|
| 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 |
326.0
|
306.2
|
| 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 |
151.8
|
150.0
|
| 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 |
142.9
|
146.1
|
| 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 |
113.6
|
98.4
|
| 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 |
99.9
|
90.4
|
| 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 |
80.5
|
78.7
|
| 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 |
68.4
|
76.3
|
| 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 |
56.3
|
60.1
|
| 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 |
402.5
|
393.0
|
| Fair value measured on a recurring basis | Collateralized loan obligations |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
345.2
|
347.0
|
| 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 |
31.9
|
32.5
|
| Fair value measured on a recurring basis | Fixed maturity investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Fixed maturity investments, at fair value |
2,886.1
|
2,770.5
|
| Fair value measured on a recurring basis | Short-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Short-term investments, at fair value |
1,501.8
|
1,881.7
|
| Fair value measured on a recurring basis | Exchange-traded funds |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
147.3
|
30.7
|
| Fair value measured on a recurring basis | Other |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
399.2
|
452.3
|
| Fair value measured on a recurring basis | Common equity securities |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
546.5
|
483.0
|
| Fair value measured on a recurring basis | Other Long-Term Investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
3,253.5
|
2,958.5
|
| 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 |
2,050.4
|
1,848.1
|
| Fair value measured on a recurring basis | Level 1 |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Total investments |
2,287.9
|
2,593.9
|
| Fair value measured on a recurring basis | Level 1 | MediaAlpha |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
166.1
|
231.2
|
| 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 |
477.7
|
460.3
|
| 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 | 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 | 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 | 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 | 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 | 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 |
477.7
|
460.3
|
| 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 |
1,496.8
|
1,871.7
|
| 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 |
147.3
|
30.7
|
| Fair value measured on a recurring basis | Level 1 | 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 |
147.3
|
30.7
|
| 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] |
|
|
| Total investments |
2,846.5
|
2,806.2
|
| 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 |
0.0
|
0.0
|
| 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 |
1,628.8
|
1,537.7
|
| 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 |
589.4
|
531.5
|
| 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 |
326.0
|
306.2
|
| 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 |
151.8
|
150.0
|
| 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 |
142.9
|
146.1
|
| 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 |
113.6
|
98.4
|
| 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 |
99.9
|
90.4
|
| 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 |
80.5
|
78.7
|
| 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 |
68.4
|
76.3
|
| 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 |
56.3
|
60.1
|
| 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 |
402.5
|
393.0
|
| 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 |
345.2
|
347.0
|
| 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 |
31.9
|
32.5
|
| 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 |
2,408.4
|
2,310.2
|
| 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 |
5.0
|
10.0
|
| 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 | Other |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Common equity securities, at fair value |
399.2
|
452.3
|
| 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 |
399.2
|
452.3
|
| 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 |
33.9
|
33.7
|
| 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 |
33.9
|
33.7
|
| Fair value measured on a recurring basis | Level 3 |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Total investments |
2,016.5
|
1,814.4
|
| 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 | 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 | 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 | 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 | 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 | 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 | 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 |
2,016.5
|
1,814.4
|
| 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 |
2,016.5
|
1,814.4
|
| Fair value measured on a recurring basis | NAV | Other long-term investments |
|
|
| Debt and Equity Securities, FV-NI [Line Items] |
|
|
| Other long-term investments |
$ 1,203.1
|
$ 1,110.4
|