Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | $ 3,077,373 | $ 2,985,161 |
Equity securities: | 616,500 | 529,631 |
Short-term investments: | 367,351 | 253,299 |
Equity contracts [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 716 | 3 |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 3,077,373 | 2,985,161 |
Equity securities: | 616,500 | 529,631 |
Short-term investments: | 367,351 | 253,299 |
Note receivable | 5,588 | 5,557 |
Assets, fair value disclosure | 4,066,812 | 3,773,648 |
Liabilities, fair value | 3,028 | 4,854 |
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 23,786 | 25,003 |
Equity securities: | 513,908 | 430,973 |
Short-term investments: | 347,482 | 236,515 |
Note receivable | 0 | 0 |
Assets, fair value disclosure | 885,176 | 692,491 |
Liabilities, fair value | 716 | 3 |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 3,053,587 | 2,960,158 |
Equity securities: | 33,739 | 31,433 |
Short-term investments: | 19,869 | 16,784 |
Note receivable | 5,588 | 5,557 |
Assets, fair value disclosure | 3,112,783 | 3,013,932 |
Liabilities, fair value | 2,312 | 4,851 |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Equity securities: | 1,213 | 1,445 |
Short-term investments: | 0 | 0 |
Note receivable | 0 | 0 |
Assets, fair value disclosure | 1,213 | 1,445 |
Liabilities, fair value | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 23,786 | 25,003 |
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 23,786 | 25,003 |
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 2,695,108 | 2,620,132 |
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 2,695,108 | 2,620,132 |
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 28,438 | 30,952 |
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 28,438 | 30,952 |
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 118,024 | 105,524 |
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 118,024 | 105,524 |
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 172,963 | 165,789 |
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 172,963 | 165,789 |
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 39,054 | 37,761 |
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 39,054 | 37,761 |
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Fixed maturity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 513,908 | 430,973 |
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 513,908 | 430,973 |
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 33,739 | 31,433 |
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 33,739 | 31,433 |
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 1,213 | 1,445 |
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 1,213 | 1,445 |
Fair Value, Measurements, Recurring [Member] | Private Equity Funds Net Asset Value [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities: | 67,640 | 65,780 |
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 52,670 | 48,256 |
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 32,801 | 31,472 |
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 19,869 | 16,784 |
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 314,681 | 205,043 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 314,681 | 205,043 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Short-term investments: | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 2,312 | 4,851 |
Liabilities, fair value | 2,312 | 4,851 |
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 2,312 | 4,851 |
Fair Value, Measurements, Recurring [Member] | Total Return Swap [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Short-term Debt [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 716 | 3 |
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Derivative liability | $ 0 | $ 0 |