Schedule II-Condensed Financial Information (Condensed Balance Sheet) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Fixed maturity securities available for sale, at fair value (amortized cost-$334,115 in 2011 and $318,190 in 2010)	$ 11,192,599	$ 10,612,552
Equity securities available for sale, at fair value (amortized cost-$9,929 in 2011 and $4,638 in 2010	362,376	466,954
Short-term investments	441,383	358,702
Other investments	570,707	567,945
Total investments	14,026,165	13,519,848
Cash and cash equivalents	1,166,713	1,150,516	1,318,552	1,040,684
Accrued investment income	153,783	147,069
Property and equipment, at cost less accumulated depreciation	242,908	267,169
Deferred income taxes, net	0	76,430
Goodwill	639,097	619,779	926,398	1,001,899
Other assets	124,298	188,454
Total assets	27,115,445	26,397,018	25,860,667
Accounts payable and other liabilities	1,486,026	1,339,582
Debt	972,278	972,164
Mandatorily redeemable preferred stock	0	5,000
Total liabilities	22,088,509	21,616,481
Common stock, par value $0.01 per share, 800,000,000 shares authorized, 88,524,374 and 102,000,371 shares outstanding at December 31, 2011 and 2010, respectively	1,464	1,453
Additional paid-in capital	3,025,477	2,993,957
Retained earnings	3,742,479	3,264,025
Accumulated other comprehensive income	554,867	285,524	65,925
Treasury stock, at cost; 57,433,178 and 43,344,638 shares at December 31, 2011 and 2010, respectively	(2,297,351)	(1,764,422)
Total stockholders' equity	5,026,936	4,780,537	4,853,249	3,709,505
Total liabilities and stockholders' equity	27,115,445	26,397,018
Fixed maturity securities available for sale, amortized cost	10,123,429	10,009,320
Equity securities available for sale, cost	357,411	452,648
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	800,000,000	800,000,000
Common stock, shares outstanding	88,524,374	102,000,371	116,648,714	117,368,534
Treasury stock, shares	57,433,178	43,344,638
Parent Company [Member]
Equity investment in subsidiaries	5,154,079	4,708,700
Fixed maturity securities available for sale, at fair value (amortized cost-$334,115 in 2011 and $318,190 in 2010)	335,614	316,832
Equity securities available for sale, at fair value (amortized cost-$9,929 in 2011 and $4,638 in 2010	11,194	5,195
Short-term investments	4,827	8,156
Other investments	65,825	79,936
Total investments	5,571,539	5,118,819
Cash and cash equivalents	497,489	656,382	727,186	302,319
Receivable from subsidiaries, net	29,442	30,550
Income tax receivable	5,948	7,635
Accrued investment income	2,899	551
Property and equipment, at cost less accumulated depreciation	118,191	137,381
Deferred income taxes, net	164,577	200,541
Other assets	23,445	32,859
Total assets	6,425,833	6,197,754
Accounts payable and other liabilities	426,619	440,053
Debt	972,278	972,164
Mandatorily redeemable preferred stock	0	5,000
Total liabilities	1,398,897	1,417,217
Commitments and Contingencies
Common stock, par value $0.01 per share, 800,000,000 shares authorized, 88,524,374 and 102,000,371 shares outstanding at December 31, 2011 and 2010, respectively	1,464	1,453
Additional paid-in capital	3,025,477	2,993,957
Retained earnings	3,742,479	3,264,025
Accumulated other comprehensive income	554,867	285,524
Treasury stock, at cost; 57,433,178 and 43,344,638 shares at December 31, 2011 and 2010, respectively	(2,297,351)	(1,764,422)
Total stockholders' equity	5,026,936	4,780,537
Total liabilities and stockholders' equity	6,425,833	6,197,754
Fixed maturity securities available for sale, amortized cost	334,115	318,190
Equity securities available for sale, cost	$ 9,929	$ 4,638
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	800,000,000	800,000,000
Common stock, shares outstanding	88,524,374	102,000,371
Treasury stock, shares	57,433,178	43,344,638