Earnings Per Share (Details) (USD $)	3 Months Ended
	Oct. 31, 2011	Oct. 31, 2010
Earnings Per Share [Abstract]
Antidilutive equity-classified stock-based awards not included in calculation of earnings per share (in shares)	2,753,000	2,927,000
Reduction in weighted average shares as a result of the repurchase of common shares	993,000	225,000
Net income for basic calculation	$ 12,601,000	$ 25,656,000
Interest expense (net of tax) on 3.0% convertible senior notes	1,117,000	1,117,000
Numerator for diluted calculation	$ 13,718,000	$ 26,773,000
Denominator for basic calculation	23,257,000	28,119,000
Dilutive effect on shares of stock options (in shares)	198,000	159,000
Dilutive effect on shares of conversion of 3.0% convertible senior notes	5,692,000	5,493,000
Denominator for diluted calculation	29,147,000	33,771,000