Stockholder's Investment (Details 2) (USD $)	12 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009	Jul. 31, 2008
Schedule of Stock Option Activity
Option Price, Lower Range, Beginning Period	$ 13.31	$ 13.31	$ 9.59
Option Price, Upper Range, Beginning Balance	$ 40.37	$ 40.37	$ 40.37
Options granted, Option Price, Lower Range	$ 28.35	$ 24.78	$ 17.23
Options granted, Option Price, Upper Range	$ 37.95	$ 33.28	$ 35.42
Options Exercises, Option Price, Lower Range	$ 14.16	$ 14.16	$ 9.59
Options Exercises, Option Price, Upper Range	$ 29.78	$ 31.54	$ 38.19
Options cancelled, Option Price, Lower Range	$ 16.39	$ 15.28	$ 20.95
Options cancelled, Option Price, Upper Range	$ 38.31	$ 38.31	$ 38.31
Option Price, Lower Range, Ending Period	$ 13.31	$ 13.31	$ 13.31
Option Price, Upper Range, Ending Balance	$ 40.37	$ 40.37	$ 40.37
Options Outstanding, Beginning Balance	5,108,736	3,980,606	3,985,205
Options Outstanding, Granted	1,365,500	1,446,500	614,000
Options Outstanding, Exercised	(417,888)	(241,403)	(138,934)
Options Outstanding, Cancelled	(330,331)	(76,967)	(479,665)
Options Outstanding, Ending Balance	5,726,017	5,108,736	3,980,606
Weighted Average Exercise Price, Granted	$ 28.86	$ 29.08	$ 21.26
Weighted Average Exercise Price, Exercised	$ 19.62	$ 18.16	$ 15.75
Weighted Average Exercise Price, Cancelled	$ 31.37	$ 31.91	$ 35.02
Weighted Average Exercise Price, Ending Balance	$ 29.24	$ 28.69	$ 27.96	$ 29.43