Segments and Other Geographic Information (Details) (USD $) In Thousands, unless otherwise specified	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
Segment Reporting Information, Profit (Loss) [Abstract]
Number of Operating Segments													2
Number of Reportable Segments After Integrated													1
Sales Revenue, Net	$ 215,443	[1]	$ 236,755	[1]	$ 207,380	[1]	$ 212,667	[1]	$ 190,468	$ 220,349	$ 176,601	$ 185,461	$ 872,246	$ 772,879	$ 743,082
Non-current Assets	621,775								592,298				621,775	592,298
United States
Segment Reporting Information, Profit (Loss) [Abstract]
Sales Revenue, Net													674,742	602,794	591,284
Non-current Assets	521,558								511,362				521,558	511,362
Canada
Segment Reporting Information, Profit (Loss) [Abstract]
Sales Revenue, Net													6,532	5,635	4,733
Non-current Assets	4,579								4,925				4,579	4,925
North America
Segment Reporting Information, Profit (Loss) [Abstract]
Sales Revenue, Net													681,274	608,429	596,017
Non-current Assets	526,137								516,287				526,137	516,287
United Kingdom
Segment Reporting Information, Profit (Loss) [Abstract]
Sales Revenue, Net													190,972	164,450	147,065
Non-current Assets	$ 95,638								$ 76,011				$ 95,638	$ 76,011

[1] Earnings per share were computed independently for each of the periods presented; therefore, the sum of the earnings per share amounts for the quarters may not equal the total for the year.