Unaudited Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data	3 Months Ended								12 Months Ended
	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011	Oct. 31, 2010	Jul. 31, 2010	Apr. 30, 2010	Jan. 31, 2010	Oct. 31, 2009	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009
Schedule of Unaudited Quarterly Financial Information
Net sales	$ 343,104	$ 337,896	$ 329,009	$ 329,588	$ 322,894	$ 321,887	$ 295,829	$ 318,486	$ 1,339,597	$ 1,259,096	$ 1,208,702
Gross margin	165,036	167,638	159,010	164,512	158,739	160,197	146,918	157,443	656,196	623,297	577,583
Operating income	42,638	40,871	37,080	41,603	34,083	35,914	23,902	35,557	162,192	129,456	120,373
Net income	29,583	28,589	24,199	26,281	21,592	23,695	15,001	21,668	108,652	81,956	70,122
Unaudited Quarterly Financial Information (Textuals) [Abstract]
Before tax restructuring charges	$ 2,202	$ 1,211	$ 2,134	$ 3,641	$ 5,717	$ 2,347	$ 3,649	$ 3,601	$ 9,188	$ 15,314	$ 25,849
Class A nonvoting common stock [Member]
Net Income Per Class A Common Share:
Basic	$ 0.56	$ 0.54	$ 0.46	$ 0.50	$ 0.41	$ 0.45	$ 0.29	$ 0.41	$ 2.06	$ 1.56	$ 1.33
Diluted	$ 0.56	$ 0.54	$ 0.46	$ 0.50	$ 0.41	$ 0.45	$ 0.29	$ 0.41	$ 2.04	$ 1.55	$ 1.32