Earnings Per Common Share (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2013	Apr. 30, 2012
Numerator for basic and diluted earnings per share:
Net income	$ 8,998,000	$ 8,174,000	$ 29,026,000	$ 21,688,000
Less income allocated to participating securities	(137,000)	(145,000)	(454,000)	(415,000)
Net income available to common shareholders	$ 8,861,000	$ 8,029,000	$ 28,572,000	$ 21,273,000
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	26,910,626	26,510,240	26,801,127	26,332,676
Dilutive effect of stock options using the treasury stock method and the average market price for the period (in shares)	172,479	289,943	210,461	302,994
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock	27,083,105	26,800,183	27,011,588	26,635,670
Basic earnings per share attributable to common stock (in dollars per share)	$ 0.33	$ 0.30	$ 1.07	$ 0.81
Diluted earnings per share attributable to common stock (in dollars per share)	$ 0.33	$ 0.30	$ 1.06	$ 0.80