Summary of Unaudited Quarterly Results (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011	Oct. 31, 2010	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Quarterly Financial Information [Line Items]
Net revenue	$ 151,011	$ 121,270	$ 126,433	$ 117,857	$ 135,349	$ 117,171	$ 117,253	$ 103,822	$ 516,571	$ 473,595	$ 414,813
Gross profit	58,561	44,752	46,845	43,026	48,975	44,160	40,809	39,019	193,184	172,963	147,897
Income from continuing operations	12,100	7,330	19,615	4,026	5,625	4,318	5,296	1,381	43,071	16,620	15,799
Income from discontinued operations								289		289	(244)
Basic net income per share	$ 0.99	$ 0.60	$ 1.61	$ 0.32	$ 0.45	$ 0.35	$ 0.42	$ 0.11	$ 3.51	$ 1.33	$ 1.26
Gain on disposal of discontinued operations								924		924
Diluted net income per share	$ 0.96	$ 0.59	$ 1.59	$ 0.32	$ 0.45	$ 0.35	$ 0.42	$ 0.11	$ 3.42	$ 1.33	$ 1.25
Net income					$ 5,625	$ 4,318	$ 5,296	$ 2,594	$ 43,071	$ 17,833	$ 15,555
Basic net income per share:
Income from continuing operations	$ 0.99	$ 0.60	$ 1.61	$ 0.32	$ 0.45	$ 0.35	$ 0.42	$ 0.11	$ 3.51	$ 1.33	$ 1.26
Income from discontinued operations, net of tax								$ 0.02		$ 0.02	$ (0.02)
Gain on disposal of discontinued operations, net of tax								$ 0.08		$ 0.08
Basic net income per share					$ 0.45	$ 0.35	$ 0.42	$ 0.21	$ 3.51	$ 1.43	$ 1.24
Diluted net income per share:
Income from continuing operations	$ 0.96	$ 0.59	$ 1.59	$ 0.32	$ 0.45	$ 0.35	$ 0.42	$ 0.11	$ 3.42	$ 1.33	$ 1.25
Income from discontinued operations, net of tax								$ 0.02		$ 0.02	$ (0.02)
Gain on disposal of discontinued operations, net of tax								$ 0.07		$ 0.07
Diluted net income per share					$ 0.45	$ 0.35	$ 0.42	$ 0.20	$ 3.42	$ 1.42	$ 1.23