Earnings Per Common Share (Details) (USD $)	3 Months Ended								12 Months Ended
	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011
Numerator for basic and diluted earnings per share:
Net income	$ 10,213,000	$ 8,998,000	$ 10,452,000	$ 9,576,000	$ 9,649,000	$ 8,174,000	$ 7,294,000	$ 6,220,000	$ 39,239,000	$ 31,337,000	$ 20,425,000
Less income allocated to participating securities									(608,000)	(580,000)	(290,000)
Net income available to common shareholders									$ 38,631,000	$ 30,757,000	$ 20,135,000
Denominator for basic and diluted earnings per share, as adjusted for participating securities:
Denominator for basic earnings per share - weighted average number of shares outstanding attributable to common stock									40,267,885	39,586,170	37,924,794
Dilutive effect of stock options using the treasury stock method and the average market price for the year (in shares)									289,007	438,753	504,747
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock									40,556,892	40,024,923	38,429,541
Basic earnings per share attributable to common stock (in dollars per share)	$ 0.25	$ 0.22	$ 0.26	$ 0.24	$ 0.24	$ 0.20	$ 0.18	$ 0.16	$ 0.96	$ 0.78	$ 0.53
Diluted earnings per share attributable to common stock (in dollars per share)	$ 0.25	$ 0.22	$ 0.25	$ 0.23	$ 0.24	$ 0.20	$ 0.18	$ 0.15	$ 0.95	$ 0.77	$ 0.52
Stock options excluded from weighted average dilutive common shares outstanding because their inclusion would have been antidilutive (in shares)											76,499