Earnings Per Common Share - Computation (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Numerator for basic and diluted earnings per share:
Net income	$ 16,291,000	$ 14,019,000	$ 15,389,000	$ 14,254,000	$ 13,273,000	$ 12,356,000	$ 11,085,000	$ 11,239,000	$ 59,953,000	$ 47,953,000	$ 43,265,000
Less income allocated to participating securities, basic									(488,000)	(433,000)	(581,000)
Net income available to common shareholders, basic									59,465,000	47,520,000	42,684,000
Less income allocated to participating securities, diluted									(488,000)	(433,000)	(581,000)
Net income available to common shareholders, diluted									$ 59,465,000	$ 47,520,000	$ 42,684,000
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									41,344,013	41,139,467	40,751,629
Dilutive effect of stock options using the treasury stock method and the average market price for the period (in shares)									46,181	63,133	159,685
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock									41,390,194	41,202,600	40,911,314
Earnings per share attributable to common stock:
Basic earnings per share (in dollars per share)	$ 0.39	$ 0.34	$ 0.37	$ 0.34	$ 0.32	$ 0.30	$ 0.27	$ 0.27	$ 1.44	$ 1.16	$ 1.05
Diluted earnings per share (in dollars per share)	$ 0.39	$ 0.34	$ 0.37	$ 0.34	$ 0.32	$ 0.30	$ 0.27	$ 0.27	$ 1.44	$ 1.15	$ 1.04