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								12 Months Ended
	Jul. 31, 2021	Apr. 30, 2021	Jan. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2021	Jul. 31, 2020	Jul. 31, 2019
Earnings Per Share [Line Items]
Net income	$ 28,027	$ 37,291	$ 30,860	$ 33,481	$ 27,685	$ 13,633	$ 33,553	$ 37,498	$ 129,659	$ 112,369
Denominator for basic earnings per share for both Class A and Class B									52,039	52,763	52,596
Plus: Effect of dilutive stock options									370	468	727
Denominator for diluted earnings per share for both Class A and Class B									52,409	53,231	53,323
Class A Nonvoting Common Stock
Earnings Per Share [Line Items]
Basic	$ 0.54	$ 0.72	$ 0.59	$ 0.64	$ 0.53	$ 0.26	$ 0.63	$ 0.71	$ 2.49	$ 2.13	$ 2.50
Diluted	$ 0.53	$ 0.71	$ 0.59	$ 0.64	$ 0.53	$ 0.26	$ 0.62	$ 0.70	$ 2.47	$ 2.11	$ 2.46
Class B Voting Common Stock
Earnings Per Share [Line Items]
Net income									$ 128,847	$ 111,531	$ 130,430
Basic									$ 2.48	$ 2.11	$ 2.48
Diluted									$ 2.46	$ 2.10	$ 2.45
Preferential Dividends on Class A Nonvoting Common Stock [Member]
Earnings Per Share [Line Items]
Cash dividends on Common Stock									$ 807	$ 828	$ 815
Preferential Dividends on Dilutive Shares [Member]
Earnings Per Share [Line Items]
Cash dividends on Common Stock									$ 5	$ 10	$ 13