Fair Value Measurements (Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2022 |
Sep. 30, 2021 |
Sep. 30, 2022 |
Sep. 30, 2021 |
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||
| Equity securities, beginning of period | $ 4,380 | $ 41,066 | $ 56,472 | $ 58,493 |
| Purchases | 0 | 18,900 | 0 | 18,900 |
| Sales | (3,528) | 0 | (56,335) | (15,015) |
| Net investment gains (losses) on Level 3 investments | 69 | (3,341) | 784 | (5,753) |
| Equity securities, end of period | $ 921 | $ 56,625 | 921 | $ 56,625 |
| Unconsolidated Markel CATCo Fund 2 [Member] | ||||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||
| Sales | $ (41,300) | |||