Consolidated Statement of Changes in Shareholders' Equity (USD $) In Thousands	Total	Common stock [Member]	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income	Treasury stock
Balance at Dec. 31, 2008
Balance at December 31, 2011 (as previously reported)	$ 3,031,183	$ 118,724	$ 914,339	$ 1,977,254	$ 119,665	$ (98,799)
Cumulative effect of accounting change (deferred policy acquisition costs)	(18,032)			(18,032)
Balance at Dec. 31, 2009	3,013,151	118,724	914,339	1,959,222	119,665	(98,799)
Net earnings	345,096			345,096
Other Comprehensive Income Loss Net Of Tax	(22,479)				(22,479)
Issuance of 2,079, 1,458 and 1,404 shares for exercise of options, including tax effect in 2012, 2011 and 2010, respectively	29,193	1,404	27,789
Purchase of 5,567, 12,645 and 1,301 common shares in 2012, 2011 and 2010, respectively	(35,124)					(35,124)
Stock-based compensation	13,018	814	12,204
Cash dividends declared $0.64, $0.60 and $0.56 per share in 2012, 2011 and 2010, respectively	(64,455)			(64,455)
Balance at Dec. 31, 2010	3,278,400	120,942	954,332	2,239,863	97,186	(133,923)
Net earnings	255,243			255,243
Other Comprehensive Income Loss Net Of Tax	130,473				130,473
Issuance of 2,079, 1,458 and 1,404 shares for exercise of options, including tax effect in 2012, 2011 and 2010, respectively	36,044	1,458	34,586
Purchase of 5,567, 12,645 and 1,301 common shares in 2012, 2011 and 2010, respectively	(373,600)					(373,600)
Stock-based compensation	12,710	320	12,390
Cash dividends declared $0.64, $0.60 and $0.56 per share in 2012, 2011 and 2010, respectively	(65,288)			(65,288)
Balance at Dec. 31, 2011	3,273,982	122,720	1,001,308	2,429,818	227,659	(507,523)
Net earnings	391,240			391,240
Other Comprehensive Income Loss Net Of Tax	67,612				67,612
Issuance of 2,079, 1,458 and 1,404 shares for exercise of options, including tax effect in 2012, 2011 and 2010, respectively	59,838	2,079	57,759
Purchase of 5,567, 12,645 and 1,301 common shares in 2012, 2011 and 2010, respectively	(178,669)					(178,669)
Stock-based compensation	7,902	315	7,587
Cash dividends declared $0.64, $0.60 and $0.56 per share in 2012, 2011 and 2010, respectively	(64,892)			(64,892)
Other	(14,401)		(14,401)
Balance at Dec. 31, 2012	$ 3,542,612	$ 125,114	$ 1,052,253	$ 2,756,166	$ 295,271	$ (686,192)