Earnings Per Common Share - Computation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Numerator for basic and diluted earnings per share:
Net income	$ 16,997	$ 17,511	$ 18,070	$ 18,800	$ 16,291	$ 14,019	$ 15,389	$ 14,254	$ 71,378	$ 59,953	$ 47,953
Less income allocated to participating securities									(431)	(488)	(433)
Net income available to common shareholders									$ 70,947	$ 59,465	$ 47,520
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 (shares)									41,468,487	41,344,013	41,139,467
Dilutive effect of stock options using the treasury stock method and the average market price for the year (shares)									74,278	46,181	63,133
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock (shares)									41,542,765	41,390,194	41,202,600
Earnings per share attributable to common stock:
Basic earnings per share (in dollars per share)	$ 0.41	$ 0.42	$ 0.43	$ 0.45	$ 0.39	$ 0.34	$ 0.37	$ 0.34	$ 1.71	$ 1.44	$ 1.16
Diluted earnings per share (in dollars per share)	$ 0.41	$ 0.42	$ 0.43	$ 0.45	$ 0.39	$ 0.34	$ 0.37	$ 0.34	$ 1.71	$ 1.44	$ 1.15
Stock options excluded from weighted average dilutive common shares outstanding because their inclusion would have been antidilutive									0	0	0