Schedule of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011
Stockholders' Equity
Outstanding at beginning of year, Shares	732,725	1,433,225	1,381,725
Exercised, Shares	(498,412)	(80,500)	(78,500)
Forfeited, Shares	(120,000)	(600,000)
Expired, Shares	(8,000)	(20,000)
Granted, Shares	0	0	130,000
Outstanding at end of year, Shares	106,313	732,725	1,433,225
Vested and expected to vest at end of year, Shares	106,313	712,725	833,225
Exercisable at year-end, Shares	106,313	566,059	609,891
Outstanding at beginning of year, Weighted-Average Exercise Price	$ 28.89	$ 30.90	$ 30.20
Exercised, Weighted-Average Exercise Price	$ 28.62	$ 17.74	$ 13.33
Forfeited, Weighted-Average Exercise Price	$ 27.84	$ 35.18
Expired, Weighted-Average Exercise Price	$ 26.91	$ 29.25
Granted, Weighted-Average Exercise Price			$ 27.72
Outstanding at end of year, Weighted-Average Exercise Price	$ 31.48	$ 28.89	$ 30.90
Vested and expected to vest at end of year, Weighted-Average Exercise Price	$ 31.48	$ 28.82	$ 27.82
Exercisable at year-end, Weighted-Average Exercise Price	$ 31.48	$ 29.24	$ 27.84