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Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | $ 4,460,115 | $ 4,115,618
Fair value | 4,729,270 | 4,312,161
Amounts in the balance sheet | 4,729,270 | 4,312,161
US Government Agencies Debt Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 13,756 | 22,502
Fair value | 13,816 | 22,637
Amounts in the balance sheet | 13,816 | 22,637
Municipal Bonds [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 2,632,559 | 2,435,346
Fair value | 2,791,212 | 2,554,208
Amounts in the balance sheet | 2,791,212 | 2,554,208
Collateralized Mortgage Backed Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 91,527 | 62,566
Fair value | 93,264 | 63,003
Amounts in the balance sheet | 93,264 | 63,003
Corporate Debt Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 240,486 | 233,730
Fair value | 241,366 | 235,565
Amounts in the balance sheet | 241,366 | 235,565
Collateralized Debt Obligations [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 256,558 | 200,656
Fair value | 256,891 | 199,218
Amounts in the balance sheet | 256,891 | 199,217
Other Debt Obligations [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 153,532 | 18,476
Fair value | 153,261 | 18,644
Amounts in the balance sheet | 153,261 | 18,645
Fixed Maturity Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 3,388,418 | 2,973,276
Fair value | 3,549,810 | 3,093,275
Amounts in the balance sheet | 3,549,810 | 3,093,275
Common Stock [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 563,394 | 498,514
Fair value | 691,782 | 586,367
Amounts in the balance sheet | 691,782 | 586,367
Nonredeemable Preferred Stock [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 31,430 | 49,442
Fair value | 32,660 | 49,708
Amounts in the balance sheet | 32,660 | 49,708
Private Equity Funds [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost |  | 1,137
Fair value |  | 1,203
Amounts in the balance sheet |  | 1,203
Private Equity Funds Net Asset Value [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 100,326 | 99,189
Fair value | 79,409 | 87,473
Amounts in the balance sheet | 79,409 | 87,473
Equity Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 695,150 | 648,282
Fair value | 803,851 | 724,751
Amounts in the balance sheet | 803,851 | 724,751
Short-term Investments [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 376,547 | 494,060
Fair value | 375,609 | 494,135
Amounts in the balance sheet | $ 375,609 | $ 494,135

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