Earnings Per Common Share - Computation (Details) - USD ($)	3 Months Ended		9 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016
Numerator for basic and diluted earnings per share:
Net income	$ 17,511,000	$ 14,019,000	$ 54,381,000	$ 43,662,000
Less income allocated to participating securities, basic	(98,000)	(115,000)	(335,000)	(359,000)
Net income available to common shareholders, basic	17,413,000	13,904,000	54,046,000	43,303,000
Less income allocated to participating securities, diluted	(98,000)	(115,000)	(335,000)	(359,000)
Net income available to common shareholders, diluted	$ 17,413,000	$ 13,904,000	$ 54,046,000	$ 43,303,000
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	41,489,587	41,363,548	41,459,067	41,335,488
Dilutive effect of stock options using the treasury stock method and the average market price for the period (in shares)	75,431	47,164	74,420	44,817
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock	41,565,018	41,410,712	41,533,487	41,380,305
Earnings per share attributable to common stock:
Basic earnings per share (in dollars per share)	$ 0.42	$ 0.34	$ 1.30	$ 1.05
Diluted earnings per share (in dollars per share)	$ 0.42	$ 0.34	$ 1.30	$ 1.05