Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	$ 5,019,561	$ 4,805,522
Fair Value	4,910,800	5,142,589
Amounts in the Balance Sheet	4,910,800	5,142,589
Fixed maturity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	4,226,790	3,909,780
Fair Value	4,088,311	4,031,523
Amounts in the Balance Sheet	4,088,311	4,031,523
U.S. government bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	159,256	13,082
Fair Value	158,607	13,085
Amounts in the Balance Sheet	158,607	13,085
Municipal securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,794,476	2,715,578
Fair Value	2,737,183	2,843,221
Amounts in the Balance Sheet	2,737,183	2,843,221
Mortgage-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	184,936	137,384
Fair Value	166,260	137,002
Amounts in the Balance Sheet	166,260	137,002
Corporate securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	607,945	529,377
Fair Value	569,553	523,853
Amounts in the Balance Sheet	569,553	523,853
Collateralized loan obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	332,859	312,928
Fair Value	320,252	314,153
Amounts in the Balance Sheet	320,252	314,153
Other asset-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	147,318	201,431
Fair Value	136,456	200,209
Amounts in the Balance Sheet	136,456	200,209
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	668,843	754,536
Fair Value	699,552	970,939
Amounts in the Balance Sheet	699,552	970,939
Common stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	463,940	561,381
Fair Value	558,169	797,024
Amounts in the Balance Sheet	558,169	797,024
Preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	64,686	64,429
Fair Value	51,236	65,501
Amounts in the Balance Sheet	51,236	65,501
Private Equity Funds Net Asset Value
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	140,217	128,726
Fair Value	90,147	108,414
Amounts in the Balance Sheet	90,147	108,414
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	123,928	141,206
Fair Value	122,937	140,127
Amounts in the Balance Sheet	$ 122,937	$ 140,127