Computation 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, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 19,314	$ 9,809	$ 15,539	$ 14,190
Weighted-average number of common shares outstanding-basic	12,417	12,294	12,430	12,304
Effect of dilutive securities:
Stock options and restricted stock units	239	287	254	270
Weighted-average number of common shares outstanding-diluted	12,656	12,581	12,684	12,574
Basic net income per share	$ 1.56	$ 0.80	$ 1.25	$ 1.15
Diluted net income per share	$ 1.53	$ 0.78	$ 1.23	$ 1.13