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Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Notes payable | $ 371,535,000 | $ 371,335,000
Unsecured debt [Member] | Borrowings [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Notes payable | 371,535,000 | 371,335,000
Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 3,839,672,000 | 3,738,293,000
Liabilities, fair value | 2,173,000 | 1,323,000
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 1,500,000 | 1,500,000
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 768,707,000 | 743,294,000
Liabilities, fair value | 780,000 | 123,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 2,998,476,000 | 2,921,995,000
Liabilities, fair value | 1,393,000 | 1,200,000
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 1,450,000 | 1,481,000
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 2,949,236,000 | 2,892,777,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | U.S. Government Bonds and Agencies [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 13,333,000 | 13,236,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Municipal Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 2,616,770,000 | 2,556,532,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Mortgage Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 32,214,000 | 27,165,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 116,401,000 | 137,542,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Collateralized Loan Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 135,453,000 | 105,202,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Other Asset-Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 35,065,000 | 53,100,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 13,333,000 | 13,236,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] | U.S. Government Bonds and Agencies [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 13,333,000 | 13,236,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] | Municipal Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] | Mortgage Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] | Collateralized Loan Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 1 [Member] | Other Asset-Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 2,935,903,000 | 2,879,541,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] | U.S. Government Bonds and Agencies [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] | Municipal Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 2,616,770,000 | 2,556,532,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] | Mortgage Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 32,214,000 | 27,165,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 116,401,000 | 137,542,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] | Collateralized Loan Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 135,453,000 | 105,202,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 2 [Member] | Other Asset-Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 35,065,000 | 53,100,000
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] | U.S. Government Bonds and Agencies [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] | Municipal Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] | Mortgage Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] | Collateralized Loan Obligations [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Fixed maturity securities [Member] | Level 3 [Member] | Other Asset-Backed Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 614,336,000 | 537,240,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Common Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 507,504,000 | 429,367,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Nonredeemable Preferred Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 34,343,000 | 34,869,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Private Equity Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 1,450,000 | 1,481,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Private Equity Funds Net Asset Value [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 71,039,000 | 71,523,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 507,504,000 | 429,367,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 1 [Member] | Common Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 507,504,000 | 429,367,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 1 [Member] | Nonredeemable Preferred Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 1 [Member] | Private Equity Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 34,343,000 | 34,869,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 2 [Member] | Common Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 2 [Member] | Nonredeemable Preferred Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 34,343,000 | 34,869,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 2 [Member] | Private Equity Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 1,450,000 | 1,481,000
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 3 [Member] | Common Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 3 [Member] | Nonredeemable Preferred Stock [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Level 3 [Member] | Private Equity Funds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 1,450,000 | 1,481,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 270,584,000 | 302,711,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Short-term Bonds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 52,666,000 | 32,018,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Money Market Instruments [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 217,918,000 | 270,693,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 247,870,000 | 300,691,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 1 [Member] | Short-term Bonds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 29,952,000 | 29,998,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 1 [Member] | Money Market Instruments [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 217,918,000 | 270,693,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 22,714,000 | 2,020,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 2 [Member] | Short-term Bonds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 22,714,000 | 2,020,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 2 [Member] | Money Market Instruments [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 3 [Member] | Short-term Bonds [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Level 3 [Member] | Money Market Instruments [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Financing Receivable [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 5,516,000 | 5,565,000
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Level 1 [Member] | Financing Receivable [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Level 2 [Member] | Financing Receivable [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 5,516,000 | 5,565,000
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Level 3 [Member] | Financing Receivable [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Assets, fair value disclosure | 0 | 0
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 1,393,000 | 1,200,000
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 1,393,000 | 1,200,000
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 780,000 | 123,000
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 780,000 | 123,000
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Unsecured debt [Member] | Borrowings [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 364,736,000 | 385,583,000
Fair Value, Measurements, Recurring [Member] | Unsecured debt [Member] | Borrowings [Member] | Level 1 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 0 | 0
Fair Value, Measurements, Recurring [Member] | Unsecured debt [Member] | Borrowings [Member] | Level 2 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | 364,736,000 | 385,583,000
Fair Value, Measurements, Recurring [Member] | Unsecured debt [Member] | Borrowings [Member] | Level 3 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Liabilities, fair value | $ 0 | $ 0

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities. + References No definition available. + Details
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- Definition Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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