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Fair Value Measurement - Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | $ 4,319,336 | $ 4,088,311
Total equity securities | 730,693 | 699,552
Note receivable | 9,974 | 0
Fair Value, Measurements, Recurring |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 4,319,336 | 4,088,311
Total equity securities | 730,693 | 699,552
Total short-term investments | 178,491 | 122,937
Note receivable | 9,974 |
Total assets at fair value | 5,238,494 | 4,910,800
Total liabilities at fair value | 1,955 | 162
Fair Value, Measurements, Recurring | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 123,182 | 103,519
Total equity securities | 597,888 | 558,169
Total short-term investments | 176,653 | 114,699
Note receivable | 0 |
Total assets at fair value | 897,723 | 776,387
Total liabilities at fair value | 1,955 | 162
Fair Value, Measurements, Recurring | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 4,196,154 | 3,984,792
Total equity securities | 51,563 | 51,236
Total short-term investments | 1,838 | 8,238
Note receivable | 9,974 |
Total assets at fair value | 4,259,529 | 4,044,266
Total liabilities at fair value | 0 | 0
Fair Value, Measurements, Recurring | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Total equity securities | 0 | 0
Total short-term investments | 0 | 0
Note receivable | 0 |
Total assets at fair value | 0 | 0
Total liabilities at fair value | 0 | 0
Fair Value, Measurements, Recurring | U.S. government bonds and agencies |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 174,450 | 158,607
Fair Value, Measurements, Recurring | U.S. government bonds and agencies | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 123,182 | 103,519
Fair Value, Measurements, Recurring | U.S. government bonds and agencies | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 51,268 | 55,088
Fair Value, Measurements, Recurring | U.S. government bonds and agencies | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Municipal securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 2,777,258 | 2,737,183
Fair Value, Measurements, Recurring | Municipal securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Municipal securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 2,777,258 | 2,737,183
Fair Value, Measurements, Recurring | Municipal securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Mortgage-backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 186,887 | 166,260
Fair Value, Measurements, Recurring | Mortgage-backed securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Mortgage-backed securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 186,887 | 166,260
Fair Value, Measurements, Recurring | Mortgage-backed securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Corporate securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 599,630 | 569,553
Fair Value, Measurements, Recurring | Corporate securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Corporate securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 599,630 | 569,553
Fair Value, Measurements, Recurring | Corporate securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Collateralized loan obligations |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 484,947 | 320,252
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 484,947 | 320,252
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Other asset-backed securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 96,164 | 136,456
Fair Value, Measurements, Recurring | Other asset-backed securities | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Other asset-backed securities | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 96,164 | 136,456
Fair Value, Measurements, Recurring | Other asset-backed securities | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total fixed maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Common stock |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 597,888 | 558,169
Fair Value, Measurements, Recurring | Common stock | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 597,888 | 558,169
Fair Value, Measurements, Recurring | Common stock | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 0 | 0
Fair Value, Measurements, Recurring | Common stock | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 0 | 0
Fair Value, Measurements, Recurring | Non-redeemable preferred stock |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 51,563 | 51,236
Fair Value, Measurements, Recurring | Non-redeemable preferred stock | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 0 | 0
Fair Value, Measurements, Recurring | Non-redeemable preferred stock | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 51,563 | 51,236
Fair Value, Measurements, Recurring | Non-redeemable preferred stock | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 0 | 0
Fair Value, Measurements, Recurring | Private equity funds measured at net asset value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total equity securities | 81,242 | 90,147
Fair Value, Measurements, Recurring | Short-term bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 13,853 | 59,876
Fair Value, Measurements, Recurring | Short-term bonds | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 12,015 | 51,638
Fair Value, Measurements, Recurring | Short-term bonds | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 1,838 | 8,238
Fair Value, Measurements, Recurring | Short-term bonds | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 0 | 0
Fair Value, Measurements, Recurring | Money market instruments |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 164,595 | 63,021
Fair Value, Measurements, Recurring | Money market instruments | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 164,595 | 63,021
Fair Value, Measurements, Recurring | Money market instruments | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 0 | 0
Fair Value, Measurements, Recurring | Money market instruments | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 0 | 0
Fair Value, Measurements, Recurring | Other |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 43 | 40
Fair Value, Measurements, Recurring | Other | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 43 | 40
Fair Value, Measurements, Recurring | Other | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 0 | 0
Fair Value, Measurements, Recurring | Other | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Total short-term investments | 0 | 0
Fair Value, Measurements, Recurring | Options sold |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Options sold | 1,955 | 162
Fair Value, Measurements, Recurring | Options sold | Level 1 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Options sold | 1,955 | 162
Fair Value, Measurements, Recurring | Options sold | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Options sold | 0 | 0
Fair Value, Measurements, Recurring | Options sold | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Options sold | $ 0 | $ 0

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- Definition Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. 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Data Type: | na
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