Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Millions |
9 Months Ended | |
|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Liability For Claims And Claims Adjustment Expense [Line Items] | ||
| (Favorable) unfavorable loss and LAE development | $ (138.5) | $ (68.3) |
| Specialty [Member] | ||
| Liability For Claims And Claims Adjustment Expense [Line Items] | ||
| (Favorable) unfavorable loss and LAE development | (51.2) | (42.4) |
| Core Commercial [Member] | ||
| Liability For Claims And Claims Adjustment Expense [Line Items] | ||
| (Favorable) unfavorable loss and LAE development | (39.3) | $ (16.5) |
| Personal Lines [Member] | ||
| Liability For Claims And Claims Adjustment Expense [Line Items] | ||
| (Favorable) unfavorable loss and LAE development | $ (48.2) | |