Earnings Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2011	Apr. 30, 2010
Earnings Per Share
Antidilutive equity-classified stock-based awards not included in calculation of earnings per share (in shares)	2,342,000	2,019,000	2,424,000	2,042,000
Net income for basic calculation	$ 14,255,000	$ 21,796,000	$ 56,007,000	$ 47,161,000
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	$ 15,372,000	$ 22,913,000	$ 59,358,000	$ 50,512,000
Denominator for basic calculation	26,577,000	28,291,000	27,310,000	28,254,000
Dilutive effect on shares of stock options	210,000	307,000	219,000	332,000
Dilutive effect on shares of conversion of 3.0% convertible senior notes	5,591,000	5,488,000	5,540,000	5,488,000
Denominator for diluted calculation	32,378,000	34,086,000	33,069,000	34,074,000