Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Net Sales	$ 697,428	$ 629,100	$ 608,834	$ 550,621	$ 684,250	$ 591,687	$ 578,680	$ 524,355	$ 2,485,983	$ 2,378,972	$ 2,341,528
Gross profit	394,382	343,551	328,176	292,641	375,357	318,573	308,843	279,158	1,358,750	1,281,931	1,241,055
Net earnings	$ 121,172	$ 84,996	$ 74,022	$ 58,051	$ 110,162	$ 74,326	$ 69,062	$ 52,544	$ 338,241	$ 306,094	$ 290,847
Basic earnings per common share:
Net earnings	$ 4.27	$ 2.96	$ 2.55	$ 1.98	$ 3.72	$ 2.49	$ 2.29	$ 1.73	$ 11.71	$ 10.22	$ 9.37
Weighted average number of common shares	28,398,579	28,732,152	29,074,695	29,370,232	29,596,949	29,818,218	30,119,889	30,299,569	28,890,771	29,945,954	31,044,532
Diluted earnings per common share:
Net earnings	$ 4.17	$ 2.89	$ 2.49	$ 1.93	$ 3.63	$ 2.43	$ 2.24	$ 1.69	$ 11.44	$ 9.96	$ 9.14
Weighted average number of common and common equivalent shares	29,045,269	29,408,614	29,750,815	30,088,245	30,366,603	30,579,954	30,849,934	31,101,979	29,571,308	30,728,482	31,824,077
Market price per share:
Common Stock Value During The Period Maximum	$ 305.89	$ 272.84	$ 253.18	$ 255.85	$ 253.27	$ 242.56	$ 228.00	$ 221.56
Common Stock Value During The Period Mimimum	$ 233.85	$ 249.99	$ 223.80	$ 231.19	$ 233.71	$ 205.55	$ 197.91	$ 196.72