Computation of Basic and Diluted net Income per Share (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
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
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 (loss) from discontinued operations, net of tax								289		289	(244)
Gain on disposal of discontinued operations, net of tax								924		924
Net income					$ 5,625	$ 4,318	$ 5,296	$ 2,594	$ 43,071	$ 17,833	$ 15,555
Weighted average number of common shares outstanding-basic									12,265	12,491	12,584
Effect of dilutive securities:
Stock options and restricted stock awards									311	81	71
Weighted average number of common shares outstanding-diluted									12,576	12,572	12,655
Basic net income (loss) 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 (loss) 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 (loss) 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 (loss) 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
Anti-dilutive shares related to outstanding stock options and unvested restricted stock awards									212	204	344