Earnings Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2012	Apr. 30, 2011
Earnings Per Share [Abstract]
Antidilutive equity-classified stock-based awards not included in calculation of earnings per share (in shares)	1,969,000	2,342,000	2,138,000	2,424,000
Reduction in weighted average shares as a result of the repurchase of common shares	458,000	232,000	3,579,000	1,086,000
Net income for basic calculation	$ 6,066,000	$ 14,255,000	$ 24,488,000	$ 56,007,000
Interest expense (net of tax) on 3.0% convertible senior notes	1,117,000	1,117,000	3,351,000	3,351,000
Numerator for diluted calculation	$ 7,183,000	$ 15,372,000	$ 27,839,000	$ 59,358,000
Denominator for basic calculation	18,853,000	26,577,000	20,746,000	27,310,000
Dilutive effect on shares of stock options (in shares)	263,000	210,000	236,000	219,000
Dilutive effect on shares of conversion of 3.0% convertible senior notes	5,794,000	5,591,000	5,742,000	5,540,000
Denominator for diluted calculation	24,910,000	32,378,000	26,724,000	33,069,000