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Fair Value Measurements (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($)
$ in Thousands
Dec. 31, 2022
Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) $ 4,088,311 $ 4,031,523
Equity securities 699,552 970,939
Fair Value, Measurements, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 4,088,311 4,031,523
Equity securities 699,552 970,939
Short-term investments 122,937 140,127
Total assets at fair value 4,910,800 5,142,589
Liabilities fair value 162 301
Fair Value, Measurements, Recurring | U.S. government bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 158,607 13,085
Fair Value, Measurements, Recurring | Municipal securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 2,737,183 2,843,221
Fair Value, Measurements, Recurring | Mortgage-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 166,260 137,002
Fair Value, Measurements, Recurring | Corporate securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 569,553 523,853
Fair Value, Measurements, Recurring | Collateralized loan obligations    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 320,252 314,153
Fair Value, Measurements, Recurring | Other asset-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 136,456 200,209
Fair Value, Measurements, Recurring | Common stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 558,169 797,024
Fair Value, Measurements, Recurring | Preferred stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 51,236 65,501
Fair Value, Measurements, Recurring | Private Equity Funds Net Asset Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 90,147 108,414
Fair Value, Measurements, Recurring | Short-term bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 59,876 17,201
Fair Value, Measurements, Recurring | Money market instruments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 63,021 122,917
Fair Value, Measurements, Recurring | Other    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 40 9
Fair Value, Measurements, Recurring | Options sold    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative liabilitly 162 301
Fair Value, Measurements, Recurring | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 103,519 13,085
Equity securities 558,169 797,024
Short-term investments 114,699 124,379
Total assets at fair value 776,387 934,488
Liabilities fair value 162 301
Fair Value, Measurements, Recurring | Level 1 | U.S. government bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 103,519 13,085
Fair Value, Measurements, Recurring | Level 1 | Municipal securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 1 | Mortgage-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 1 | Corporate securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 1 | Collateralized loan obligations    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 1 | Other asset-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 1 | Common stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 558,169 797,024
Fair Value, Measurements, Recurring | Level 1 | Preferred stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0 0
Fair Value, Measurements, Recurring | Level 1 | Short-term bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 51,638 1,453
Fair Value, Measurements, Recurring | Level 1 | Money market instruments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 63,021 122,917
Fair Value, Measurements, Recurring | Level 1 | Other    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 40 9
Fair Value, Measurements, Recurring | Level 1 | Options sold    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative liabilitly 162 301
Fair Value, Measurements, Recurring | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 3,984,792 4,018,438
Equity securities 51,236 65,501
Short-term investments 8,238 15,748
Total assets at fair value 4,044,266 4,099,687
Liabilities fair value 0 0
Fair Value, Measurements, Recurring | Level 2 | U.S. government bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 55,088 0
Fair Value, Measurements, Recurring | Level 2 | Municipal securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 2,737,183 2,843,221
Fair Value, Measurements, Recurring | Level 2 | Mortgage-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 166,260 137,002
Fair Value, Measurements, Recurring | Level 2 | Corporate securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 569,553 523,853
Fair Value, Measurements, Recurring | Level 2 | Collateralized loan obligations    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 320,252 314,153
Fair Value, Measurements, Recurring | Level 2 | Other asset-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 136,456 200,209
Fair Value, Measurements, Recurring | Level 2 | Common stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0 0
Fair Value, Measurements, Recurring | Level 2 | Preferred stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 51,236 65,501
Fair Value, Measurements, Recurring | Level 2 | Short-term bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 8,238 15,748
Fair Value, Measurements, Recurring | Level 2 | Money market instruments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 0 0
Fair Value, Measurements, Recurring | Level 2 | Other    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 0 0
Fair Value, Measurements, Recurring | Level 2 | Options sold    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative liabilitly 0 0
Fair Value, Measurements, Recurring | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Equity securities 0 0
Short-term investments 0 0
Total assets at fair value 0 0
Liabilities fair value 0 0
Fair Value, Measurements, Recurring | Level 3 | U.S. government bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 3 | Municipal securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 3 | Mortgage-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 3 | Corporate securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 3 | Collateralized loan obligations    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 3 | Other asset-backed securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed maturity securities (amortized cost $4,226,790; $3,909,780) 0 0
Fair Value, Measurements, Recurring | Level 3 | Common stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0 0
Fair Value, Measurements, Recurring | Level 3 | Preferred stock    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Equity securities 0 0
Fair Value, Measurements, Recurring | Level 3 | Short-term bonds    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 0 0
Fair Value, Measurements, Recurring | Level 3 | Money market instruments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 0 0
Fair Value, Measurements, Recurring | Level 3 | Other    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term investments 0 0
Fair Value, Measurements, Recurring | Level 3 | Options sold    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative liabilitly $ 0 $ 0