Schedule II - Condensed Financial Information Of Registrant (Condensed Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009	Dec. 31, 2008
Long-term investments	$ 26,167		$ 42,985
Total investments	12,353,586		11,197,977
Cash	84,113		365,679
Other assets	391,076		378,700
Total assets	17,156,391		16,159,762
Short-term debt	224,842		198,875
Long-term debt	790,571		789,643
Due to affiliates	124,421		124,421
Other liabilities	312,417		284,062
Total liabilities	12,927,483		12,143,521
Preferred stock	0		0
Common stock	112,312	[1]	119,812	[1]
Additional paid-in capital	425,331		432,608
Accumulated other comprehensive income	549,423		22,958
Retained earnings	3,634,481	[1]	3,473,482	[1]
Treasury stock	(492,639)		(32,619)
Total shareholders' equity	4,228,908		4,016,241		3,398,891	2,222,907
Total liabilities and shareholders' equity	17,156,391		16,159,762
Parent Company [Member]
Long-term investments	36,458		15,963
Short-term investments, condensed balance sheet	58		62,582
Total investments	36,516		78,545
Cash	27,099		0
Investment in affiliates	5,329,769		4,973,495
Due from affiliates	50,977		138,130
Taxes receivable	61,616		65,195
Other assets	7,581		5,391
Total assets	5,513,558		5,260,756
Short-term debt	224,842		198,875
Long-term debt	790,571		789,643
Due to affiliates	145,556		136,931
Other liabilities	123,681		119,066
Total liabilities	1,284,650		1,244,515
Preferred stock	351		351
Common stock	112,312		119,812
Additional paid-in capital	775,842		783,119
Accumulated other comprehensive income	549,423		22,958
Retained earnings	3,634,481		3,473,482
Treasury stock	(843,501)		(383,481)
Total shareholders' equity	4,228,908		4,016,241
Total liabilities and shareholders' equity	$ 5,513,558		$ 5,260,756

[1] Amounts have been retroactively adjusted for stock split described in Note 1.