Investments (Available-For-Sale Investments) (Details) (USD $) In Thousands | Sep. 30, 2011 | Dec. 31, 2010 |
|---|
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | $ 5,223,979 | $ 5,256,980 |
| Equity securities, Amortized Cost | 1,092,662 | 996,088 |
| Available-for-sale securities, Amortized Cost | 6,808,371 | 6,578,404 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 904,292 | 956,338 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (22,484) | (36,634) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | (12,640) | (19,571) |
| Total fixed maturities, Estimated Fair Value | 5,576,584 | 5,431,226 |
| Available-for-sale equity investments, Estimated Fair Value | 1,609,199 | 1,721,971 |
| Short-term investments, Estimated Fair Value | 491,756 | 325,340 |
| Available-for-sale investments, Estimated Fair Value | 7,677,539 | 7,478,537 |
U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 284,438 | 300,555 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 23,733 | 20,832 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (12) | (49) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Total fixed maturities, Estimated Fair Value | 308,159 | 321,338 |
Obligations Of States, Municipalities And Political Subdivisions [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 2,743,359 | 2,767,169 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 176,163 | 61,620 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (1,359) | (29,450) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Total fixed maturities, Estimated Fair Value | 2,918,163 | 2,799,339 |
Foreign Governments [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 683,747 | 550,755 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 56,616 | 24,662 |
| Available-for-sale investments, Gross Unrealized Holding Losses | 0 | (2,599) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Total fixed maturities, Estimated Fair Value | 740,363 | 572,818 |
Residential Mortgage-Backed Securities [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 392,534 | 409,415 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 31,355 | 29,664 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (13) | (1,738) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | (5,922) | (11,778) |
| Total fixed maturities, Estimated Fair Value | 417,954 | 425,563 |
Asset-Backed Securities [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 16,723 | 21,704 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 837 | 1,052 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (8) | 0 |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Total fixed maturities, Estimated Fair Value | 17,552 | 22,756 |
Public Utilities [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 70,482 | 95,770 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 5,625 | 6,674 |
| Available-for-sale investments, Gross Unrealized Holding Losses | 0 | 0 |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Total fixed maturities, Estimated Fair Value | 76,107 | 102,444 |
Convertible Bonds [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | | 16,725 |
| Available-for-sale investments, Gross Unrealized Holding Gains | | 0 |
| Available-for-sale investments, Gross Unrealized Holding Losses | | 0 |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | | 0 |
| Total fixed maturities, Estimated Fair Value | | 16,725 |
All Other Corporate Bonds [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 1,032,696 | 1,094,887 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 74,636 | 83,752 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (2,328) | (603) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | (6,718) | (7,793) |
| Total fixed maturities, Estimated Fair Value | 1,098,286 | 1,170,243 |
Fixed Maturities [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Fixed maturities, Amortized Cost | 5,223,979 | 5,256,980 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 368,965 | 228,256 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (3,720) | (34,439) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | (12,640) | (19,571) |
| Total fixed maturities, Estimated Fair Value | 5,576,584 | 5,431,226 |
Insurance Companies, Banks And Trusts [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Equity securities, Amortized Cost | 371,004 | 388,848 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 250,441 | 323,634 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (9,050) | (1,496) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Available-for-sale equity investments, Estimated Fair Value | 612,395 | 710,986 |
Industrial, Consumer And All Other [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Equity securities, Amortized Cost | 721,658 | 607,240 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 284,859 | 404,444 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (9,713) | (699) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Available-for-sale equity investments, Estimated Fair Value | 996,804 | 1,010,985 |
Equity Securities [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Equity securities, Amortized Cost | 1,092,662 | 996,088 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 535,300 | 728,078 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (18,763) | (2,195) |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Available-for-sale equity investments, Estimated Fair Value | 1,609,199 | 1,721,971 |
Short-Term Investments [Member] | | |
| Schedule of Available-for-sale Securities [Line Items] | | |
| Short-term investments, Amortized Cost | 491,730 | 325,336 |
| Available-for-sale investments, Gross Unrealized Holding Gains | 27 | 4 |
| Available-for-sale investments, Gross Unrealized Holding Losses | (1) | 0 |
| Available-for-sale investments, Unrealized Other-Than-Temporary Impairment Losses | 0 | 0 |
| Short-term investments, Estimated Fair Value | $ 491,756 | $ 325,340 |