Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Net Sales	$ 657,292	$ 648,360	$ 578,553	$ 570,283	$ 535,400	$ 601,114	$ 561,088	$ 498,766	$ 2,341,528	$ 2,309,328	$ 1,968,178
Gross profit	356,788	346,159	308,157	299,008	277,102	314,417	296,191	261,507	1,241,055	1,218,274	1,037,196
Net earnings	$ 104,633	$ 94,282	$ 72,183	$ 61,704	$ 52,327	$ 68,196	$ 60,188	$ 46,827	$ 290,847	$ 269,493	$ 232,148
Basic earnings per common share:
Net earnings	$ 3.43	$ 2.99	$ 2.34	$ 1.97	$ 1.66	$ 2.15	$ 1.88	$ 1.45	$ 9.37	$ 8.45	$ 6.98
Weighted average number of common shares	30,532,491	31,542,400	30,846,062	31,267,660	31,531,915	31,760,270	31,997,850	32,290,595	31,044,532	31,897,779	33,280,463
Diluted earnings per common share:
Net earnings	$ 3.35	$ 2.91	$ 2.28	$ 1.93	$ 1.62	$ 2.09	$ 1.82	$ 1.41	$ 9.14	$ 8.21	$ 6.80
Weighted average number of common and common equivalent shares	31,271,377	32,387,459	31,599,081	32,038,928	32,386,924	32,664,482	33,013,887	33,291,632	31,824,077	32,839,365	34,140,097
Market price per share:
Common Stock Value During The Period Maximum		$ 167.13				$ 175.28	$ 191.95	$ 177.07
Common Stock Value During The Period Mimimum		$ 130.12				$ 131.91	$ 157.13	$ 147.23