Summary Of Investments Other Than Investments In Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 3,502,880	$ 3,303,156
Fair value	3,547,560	3,380,642
Amounts in the balance sheet	3,547,560	3,380,642
Fixed Maturity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,795,410	2,804,275
Fair value	2,814,553	2,880,003
Amounts in the balance sheet	2,814,554	2,880,003
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	12,288	22,542
Fair value	12,275	22,507
Amounts in the balance sheet	12,275	22,507
Fixed Maturity Securities [Member] \| Municipal Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,432,181	2,417,046
Fair value	2,449,292	2,505,039
Amounts in the balance sheet	2,449,292	2,505,039
Fixed Maturity Securities [Member] \| Collateralized Mortgage Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	39,082	49,639
Fair value	39,777	49,839
Amounts in the balance sheet	39,778	49,839
Fixed Maturity Securities [Member] \| Corporate Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	189,780	255,606
Fair value	189,688	243,372
Amounts in the balance sheet	189,688	243,372
Fixed Maturity Securities [Member] \| Collateralized Debt Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	85,429	50,710
Fair value	86,525	50,548
Amounts in the balance sheet	86,525	50,548
Fixed Maturity Securities [Member] \| Other asset-backed securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	36,650	8,732
Fair value	36,996	8,698
Amounts in the balance sheet	36,996	8,698
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	331,770	313,528
Fair value	357,327	315,362
Amounts in the balance sheet	357,326	315,362
Equity Securities [Member] \| Common Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	286,503	275,479
Fair value	316,450	280,263
Amounts in the balance sheet	316,449	280,263
Equity Securities [Member] \| Nonredeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	32,436	25,161
Fair value	31,809	24,668
Amounts in the balance sheet	31,809	24,668
Equity Securities [Member] \| Private Credit Fund [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	12,831	12,888
Fair value	9,068	10,431
Amounts in the balance sheet	9,068	10,431
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	375,700	185,353
Fair value	375,680	185,277
Amounts in the balance sheet	$ 375,680	$ 185,277

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.

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

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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.

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