Calculation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jan. 31, 2013		Jan. 31, 2012		Jan. 31, 2013		Jan. 31, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 9,809		$ 19,615		$ 14,190		$ 23,641
Weighted average number of common shares outstanding-basic	12,294		12,188		12,304		12,464
Effect of dilutive securities:
Stock options and RSUs	287		145		270		131
Weighted average number of common shares outstanding-diluted	12,581		12,333		12,574		12,595
Basic net income per share	$ 0.80		$ 1.61		$ 1.15		$ 1.90
Diluted net income per share	$ 0.78		$ 1.59		$ 1.13		$ 1.88
Anti-dilutive shares related to outstanding stock options and unvested RSUs	110	[1]	239	[1]	89	[1]	253	[1]

[1] Certain outstanding stock options were not included in the computation of diluted income per share because the options' exercise prices were greater than the average market price of the common stock and, therefore, the effect would be anti-dilutive. Certain RSUs were also excluded from the computation as their effect would be anti-dilutive.