Schedule of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Stockholders' Equity
Outstanding at beginning of year, Shares	1,433,225	1,381,725	513,561
Exercised, Shares	(80,500)	(78,500)	(586)
Forfeited, Shares	(600,000)
Expired, Shares	(20,000)		(1,250)
Granted, Shares		130,000	870,000
Outstanding at end of year, Shares	732,725	1,433,225	1,381,725
Vested and expected to vest at end of year, Shares	712,725	833,225	1,381,725
Exercisable at year-end, Shares	566,059	609,891	445,057
Outstanding at beginning of year, Weighted-Average Exercise Price	$ 30.90	$ 30.20	$ 23.47
Exercised, Weighted-Average Exercise Price	$ 17.74	$ 13.33	$ 26.91
Forfeited, Weighted-Average Exercise Price	$ 35.18
Expired, Weighted-Average Exercise Price	$ 29.25		$ 27.40
Granted, Weighted-Average Exercise Price		$ 27.72	$ 34.17
Outstanding at end of year, Weighted-Average Exercise Price	$ 28.89	$ 30.90	$ 30.20
Vested and expected to vest at end of year, Weighted-Average Exercise Price	$ 28.82	$ 27.82	$ 30.20
Exercisable at year-end, Weighted-Average Exercise Price	$ 29.24	$ 27.84	$ 22.99