Recent Accounting Pronouncements Recent Accounting Pronouncements (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred policy acquisition costs	$ 425,070		$ 404,047
Stockholders equity	4,378,541		4,306,217
Other operating expenses	481,604	431,779
Income before income taxes	160,223	187,303	701,928	513,086	598,910
Federal and foreign income taxes	(43,625)	(52,071)
Net Income (Loss)	$ 116,615	$ 135,318	$ 510,592	$ 391,211	$ 446,405
Earnings Per Share, Basic	$ 0.86	$ 0.98
Earnings Per Share, Diluted	$ 0.83	$ 0.94