Earnings Per Common Share - Computation (Details) - USD ($)	3 Months Ended
	Oct. 31, 2016	Oct. 31, 2015
Numerator for basic and diluted earnings per share:
Net income	$ 18,800,000	$ 14,254,000
Less income allocated to participating securities, basic	(134,000)	(118,000)
Net income available to common shareholders, basic	18,666,000	14,136,000
Less income allocated to participating securities, diluted	(134,000)	(118,000)
Net income available to common shareholders, diluted	$ 18,666,000	$ 14,136,000
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	41,403,050	41,283,245
Dilutive effect of stock options using the treasury stock method and the average market price for the period (in shares)	72,015	38,875
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock	41,475,065	41,322,120
Earnings per share attributable to common stock:
Basic earnings per share (in dollars per share)	$ 0.45	$ 0.34
Diluted earnings per share (in dollars per share)	$ 0.45	$ 0.34
Stock options excluded from weighted average dilutive common shares outstanding because their inclusion would have been antidilutive (in shares)		15,000