Earnings Per Share (Details) (USD $)	3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011
Earnings Per Share [Abstract]
Antidilutive equity-classified stock-based awards not included in calculation of diluted earnings per share (in shares)	2,382,000	2,753,000
Reduction in weighted average shares as a result of the repurchase of common shares		993,000
Net income for basic calculation	$ 7,435,000	$ 12,601,000
Interest expense (net of tax) on 3.0% convertible senior notes	1,117,000	1,117,000
Numerator for diluted calculation	$ 8,552,000	$ 13,718,000
Denominator for basic calculation (in shares)	17,379,000	23,257,000
Dilutive effect on shares of stock options (in shares)	159,000	198,000
Dilutive effect on shares of conversion of 3.0% convertible senior notes (in shares)	5,906,000	5,692,000
Denominator for diluted calculation (in shares)	23,444,000	29,147,000