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Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | $ 3,600,120 | $ 3,502,880
Fair value | 3,732,728 | 3,547,560
Amounts in the balance sheet | 3,732,728 | 3,547,560
Fixed Maturity Securities [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 2,823,230 | 2,795,410
Fair value | 2,892,777 | 2,814,553
Amounts in the balance sheet | 2,892,777 | 2,814,553
Fixed Maturity Securities [Member] | U.S. Government Bonds And Agencies [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 13,355 | 12,288
Fair value | 13,236 | 12,275
Amounts in the balance sheet | 13,236 | 12,275
Fixed Maturity Securities [Member] | Municipal Securities [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 2,490,150 | 2,432,181
Fair value | 2,556,532 | 2,449,292
Amounts in the balance sheet | 2,556,532 | 2,449,292
Fixed Maturity Securities [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 26,454 | 39,082
Fair value | 27,165 | 39,777
Amounts in the balance sheet | 27,165 | 39,777
Fixed Maturity Securities [Member] | Corporate Debt Securities [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 136,013 | 189,780
Fair value | 137,542 | 189,688
Amounts in the balance sheet | 137,542 | 189,688
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 104,323 | 85,429
Fair value | 105,202 | 86,525
Amounts in the balance sheet | 105,202 | 86,525
Fixed Maturity Securities [Member] | Other asset-backed securities [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 52,935 | 36,650
Fair value | 53,100 | 36,996
Amounts in the balance sheet | 53,100 | 36,996
Equity Securities [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 474,197 | 331,770
Fair value | 537,240 | 357,327
Amounts in the balance sheet | 537,240 | 357,327
Equity Securities [Member] | Common Stock [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 368,619 | 286,503
Fair value | 429,367 | 316,450
Amounts in the balance sheet | 429,367 | 316,450
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 34,429 | 32,436
Fair value | 34,869 | 31,809
Amounts in the balance sheet | 34,869 | 31,809
Equity Securities [Member] | Private Equity Funds [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 1,481 | 12,831
Fair value | 1,481 | 9,068
Amounts in the balance sheet | 1,481 | 9,068
Equity Securities [Member] | Private Equity Funds, Net Asset Value [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 69,668 |
Fair value | 71,523 |
Amounts in the balance sheet | 71,523 |
Short-term Investments [Member] |  |
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] |  |
Cost | 302,693 | 375,700
Fair value | 302,711 | 375,680
Amounts in the balance sheet | $ 302,711 | $ 375,680

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- Definition This element represents the carrying (reported) amount of the entity's investments as of the balance sheet date. This amount may represent the individual investment's or group of similar investments' original cost, fair value, or such other amount at which the investment is shown in the entity's balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 7 -Subparagraph (SX 210.12-15) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010 + Details
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- Definition This item represents the original cost of the entity's investments including investments in equity securities and, as to fixed maturities, original cost reduced by repayments and adjusted for amortization of premiums or accrual of discounts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 7 -Subparagraph (SX 210.12-15) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010 + Details
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- Definition This item represents the reported amount of the entity's investments measured at fair value. Fair value is the price that would be received to sell an investment in an orderly transaction between market participants at the balance sheet [measurement] date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 7 -Subparagraph (SX 210.12-15) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010 + Details
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