Net Income per Common Share - Reconciliation of Numerator and Denominator of Basic and Diluted Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Earnings Per Share [Line Items]
Net income	$ 33,553	$ 29,227	$ 71,051	$ 59,864
Denominator for basic earnings per share for both Class A and Class B	53,320	52,532	53,232	52,366
Plus: Effect of dilutive stock options	507	674	549	716
Denominator for diluted earnings per share for both Class A and Class B	53,827	53,206	53,781	53,082
Class A nonvoting common stock
Earnings Per Share [Line Items]
Net earnings per share, basic	$ 0.63	$ 0.56	$ 1.33	$ 1.14
Net earnings per share, diluted	$ 0.62	$ 0.55	$ 1.32	$ 1.13
Class B voting common stock
Earnings Per Share [Line Items]
Preferential dividends	$ 0	$ 0	$ 828	$ 815
Preferential dividends on dilutive stock options	0	0	10	(13)
Numerator for basic and diluted earnings per Class B Voting Common Share	$ 33,553	$ 29,227	$ 70,213	$ 59,036
Net earnings per share, basic	$ 0.63	$ 0.56	$ 1.32	$ 1.13
Net earnings per share, diluted	$ 0.62	$ 0.55	$ 1.31	$ 1.11