Earnings Per Common Share - Computation (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Numerator for basic and diluted earnings per share:
Net income	$ 18,070,000	$ 15,389,000	$ 36,870,000	$ 29,643,000
Less income allocated to participating securities, basic	(103,000)	(126,000)	(237,000)	(244,000)
Net income available to common shareholders, basic	17,967,000	15,263,000	36,633,000	29,399,000
Less income allocated to participating securities, diluted	(103,000)	(126,000)	(237,000)	(244,000)
Net income available to common shareholders, diluted	$ 17,967,000	$ 15,263,000	$ 36,633,000	$ 29,399,000
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	41,485,557	41,360,279	41,444,304	41,321,762
Dilutive effect of stock options using the treasury stock method and the average market price for the period (in shares)	74,582	44,096	73,279	42,727
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock	41,560,139	41,404,375	41,517,583	41,364,489
Earnings per share attributable to common stock:
Basic earnings per share (in dollars per share)	$ 0.43	$ 0.37	$ 0.88	$ 0.71
Diluted earnings per share (in dollars per share)	$ 0.43	$ 0.37	$ 0.88	$ 0.71
Stock options excluded from weighted average dilutive common shares outstanding because their inclusion would have been antidilutive (in shares)		15,000