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Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
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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Amount of investment held by insurance company, excluding investment in related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-SubTopic 320
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