Unaudited Quarterly Financial Data (Details) (USD $)	3 Months Ended												12 Months Ended
	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	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, 2012		Jul. 31, 2011		Jul. 31, 2010
Selected Quarterly Financial Information [Abstract]
Net sales	$ 112,775,000	$ 99,793,000	$ 99,141,000	$ 113,361,000	$ 140,327,000	$ 131,081,000	$ 162,811,000	$ 178,160,000	$ 256,954,000	$ 216,303,000	$ 171,132,000	$ 133,816,000	$ 425,070,000		$ 612,379,000		$ 778,205,000
Gross profit	49,135,000	41,678,000	41,416,000	51,280,000	58,931,000	56,971,000	60,910,000	64,234,000	82,532,000	74,791,000	63,501,000	49,774,000	183,509,000		241,046,000		270,598,000
Net income	$ 7,928,000	$ 6,066,000	$ 5,821,000	$ 12,601,000	$ 11,888,000	$ 14,255,000	$ 16,096,000	$ 25,656,000	$ 13,469,000	$ 21,796,000	$ 16,333,000	$ 9,032,000	$ 32,416,000		$ 67,895,000		$ 60,630,000
Diluted income per share	$ 0.38	$ 0.29	$ 0.27	$ 0.47	$ 0.42	$ 0.47	$ 0.52	$ 0.79	$ 0.43	$ 0.67	$ 0.51	$ 0.30	$ 1.42	[1]	$ 2.22	[1]	$ 1.91	[1]

[1] * Income per share information for the full fiscal year may not equal the total of the quarters within the year.