Summary of Significant Accounting and Reporting Policies (Earnings Per Share) (Details) (USD $)	3 Months Ended												12 Months Ended
	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011	Oct. 31, 2010	Jul. 31, 2010	Apr. 30, 2010	Jan. 31, 2010	Oct. 31, 2009	Jul. 31, 2009	Apr. 30, 2009	Jan. 31, 2009	Oct. 31, 2008	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009
Summary of Significant Accounting and Reporting Policies [Abstract]
Antidilutive equity-classified stock-based awards not included in calculation of earnings per share (in shares)													2,486,000	2,148,000	1,435,000
Reduction in weighted average shares as a result of the repurchase of common shares													1,781,000
Net income for basic calculation	$ 11,888,000	$ 14,255,000	$ 16,096,000	$ 25,656,000	$ 13,469,000	$ 21,796,000	$ 16,333,000	$ 9,032,000	$ 6,178,000	$ 7,610,000	$ 12,096,000	$ 21,641,000	$ 67,895,000	$ 60,630,000	$ 47,525,000
Interest expense (net of tax) on 2.0% convertible senior notes															2,866,000
Interest expense (net of tax) on 3.0% convertible senior notes													4,468,000	4,468,000	1,030,000
Numerator for diluted calculation													$ 72,363,000	$ 65,098,000	$ 51,421,000
Denominator for basic calculation (in shares)													26,842,000	28,270,000	26,321,000
Dilutive effect on shares of stock options (in shares)													215,000	316,000	448,000
Dilutive effect on shares of conversion of 2.0% senior notes (in shares)															1,756,000
Dilutive effect on shares of conversion of 3.0% convertible senior notes													5,566,000	5,488,000	1,268,000
Denominator for diluted calculation													32,623,000	34,074,000	29,793,000