Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) | Sep. 30, 2018 | Dec. 31, 2017 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Notes payable | $ 371,635,000 | $ 371,335,000 |
Unsecured debt [Member] | Borrowings [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Notes payable | 371,635,000 | 371,335,000 |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, fair value disclosure | 3,909,578,000 | 3,738,293,000 |
Liabilities, fair value | 1,550,000 | 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 | 1,400,000 | 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 | 836,714,000 | 743,294,000 |
Liabilities, fair value | 589,000 | 123,000 |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, fair value disclosure | 3,001,954,000 | 2,921,995,000 |
Liabilities, fair value | 961,000 | 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 | 1,446,000 | 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 | 2,952,871,000 | 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 | 14,105,000 | 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 | 2,590,847,000 | 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 | 31,513,000 | 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 | 119,292,000 | 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 | 155,796,000 | 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 | 41,318,000 | 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 | 14,105,000 | 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 | 14,105,000 | 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 | 2,938,766,000 | 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 | 2,590,847,000 | 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 | 31,513,000 | 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 | 119,292,000 | 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 | 155,796,000 | 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 | 41,318,000 | 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 | 688,387,000 | 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 | 583,851,000 | 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 | 33,626,000 | 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 | 1,446,000 | 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 | 69,464,000 | 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 | 583,851,000 | 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 | 583,851,000 | 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 | 33,626,000 | 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 | 33,626,000 | 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 | 1,446,000 | 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 | 1,446,000 | 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 | 262,806,000 | 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 | 55,496,000 | 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 | 207,310,000 | 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 | 238,758,000 | 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 | 31,448,000 | 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 | 207,310,000 | 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 | 24,048,000 | 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 | 24,048,000 | 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 | 5,514,000 | 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 | 5,514,000 | 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 | 961,000 | 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 | 961,000 | 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 | 589,000 | 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 | 589,000 | 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 | 361,118,000 | 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 | 361,118,000 | 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 |