Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	$ 4,805,522	$ 4,460,115
Fair Value	5,142,589	4,729,270
Amounts in the Balance Sheet	5,142,589	4,729,270
Fixed maturity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	3,909,780	3,388,418
Fair Value	4,031,523	3,549,810
Amounts in the Balance Sheet	4,031,523	3,549,810
U.S. government bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	13,082	13,756
Fair Value	13,085	13,816
Amounts in the Balance Sheet	13,085	13,816
Municipal securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,715,578	2,632,559
Fair Value	2,843,221	2,791,212
Amounts in the Balance Sheet	2,843,221	2,791,212
Mortgage-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	137,384	91,527
Fair Value	137,002	93,264
Amounts in the Balance Sheet	137,002	93,264
Corporate securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	529,377	240,486
Fair Value	523,853	241,366
Amounts in the Balance Sheet	523,853	241,366
Collateralized loan obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	312,928	256,558
Fair Value	314,153	256,891
Amounts in the Balance Sheet	314,153	256,891
Other asset-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	201,431	153,532
Fair Value	200,209	153,261
Amounts in the Balance Sheet	200,209	153,261
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	754,536	695,150
Fair Value	970,939	803,851
Amounts in the Balance Sheet	970,939	803,851
Common stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	561,381	563,394
Fair Value	797,024	691,782
Amounts in the Balance Sheet	797,024	691,782
Non-redeemable preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	64,429	31,430
Fair Value	65,501	32,660
Amounts in the Balance Sheet	65,501	32,660
Private Equity Funds Net Asset Value
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	128,726	100,326
Fair Value	108,414	79,409
Amounts in the Balance Sheet	108,414	79,409
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	141,206	376,547
Fair Value	140,127	375,609
Amounts in the Balance Sheet	$ 140,127	$ 375,609