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Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | $ 4,115,618 | $ 3,768,141
Fair value | 4,312,161 | 3,768,091
Amounts in the balance sheet | 4,312,161 | 3,768,091
US Government Agencies Debt Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 22,502 | 25,131
Fair value | 22,637 | 25,003
Amounts in the balance sheet | 22,637 | 25,003
Municipal Bonds [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 2,435,346 | 2,599,056
Fair value | 2,554,208 | 2,620,132
Amounts in the balance sheet | 2,554,208 | 2,620,132
Collateralized Mortgage Backed Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 62,566 | 30,640
Fair value | 63,003 | 30,952
Amounts in the balance sheet | 63,003 | 30,952
Corporate Debt Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 233,730 | 107,479
Fair value | 235,565 | 105,524
Amounts in the balance sheet | 235,565 | 105,524
Collateralized Debt Obligations [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 200,656 | 169,626
Fair value | 199,218 | 165,789
Amounts in the balance sheet | 199,217 | 165,789
Other Debt Obligations [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 18,476 | 37,609
Fair value | 18,644 | 37,761
Amounts in the balance sheet | 18,645 | 37,761
Fixed Maturity Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 2,973,276 | 2,969,541
Fair value | 3,093,275 | 2,985,161
Amounts in the balance sheet | 3,093,275 | 2,985,161
Common Stock [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 498,514 | 438,504
Fair value | 586,367 | 430,973
Amounts in the balance sheet | 586,367 | 430,973
Nonredeemable Preferred Stock [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 49,442 | 34,429
Fair value | 49,708 | 31,433
Amounts in the balance sheet | 49,708 | 31,433
Private Equity Funds [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 1,137 | 1,481
Fair value | 1,203 | 1,445
Amounts in the balance sheet | 1,203 | 1,445
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 | 99,189 | 69,668
Fair value | 87,473 | 65,780
Amounts in the balance sheet | 87,473 | 65,780
Equity Securities [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 648,282 | 544,082
Fair value | 724,751 | 529,631
Amounts in the balance sheet | 724,751 | 529,631
Short-term Investments [Member] |  |
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] |  |
Cost | 494,060 | 254,518
Fair value | 494,135 | 253,299
Amounts in the balance sheet | $ 494,135 | $ 253,299

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