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, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018
Earnings Per Share [Line Items]
Net income	$ 27,685	$ 13,633	$ 33,553	$ 37,498	$ 36,613	$ 34,781	$ 29,227	$ 30,637	$ 112,369	$ 131,258
Cash dividends on Common Stock									$ 45,756	$ 44,732	$ 42,873
Denominator for basic earnings per share for both Class A and Class B									52,763	52,596	51,677
Plus: Effect of dilutive stock options									468	727	847
Denominator for diluted earnings per share for both Class A and Class B									53,231	53,323	52,524
Class A Nonvoting Common Stock [Member]
Earnings Per Share [Line Items]
Net income per share, basic	$ 0.53	$ 0.26	$ 0.63	$ 0.71	$ 0.69	$ 0.66	$ 0.56	$ 0.59	$ 2.13	$ 2.50	$ 1.76
Net income per share, diluted	$ 0.53	$ 0.26	$ 0.62	$ 0.70	$ 0.68	$ 0.65	$ 0.55	$ 0.58	$ 2.11	$ 2.46	$ 1.73
Class B Voting Common Stock [Member]
Earnings Per Share [Line Items]
Net income									$ 111,531	$ 130,430	$ 90,247
Net income per share, basic									$ 2.11	$ 2.48	$ 1.75
Net income per share, diluted									$ 2.10	$ 2.45	$ 1.72
Preferential Dividends on Class A Nonvoting Common Stock [Member]
Earnings Per Share [Line Items]
Cash dividends on Common Stock									$ 828	$ 815	$ 799
Preferential Dividends on Dilutive Shares [Member]
Earnings Per Share [Line Items]
Cash dividends on Common Stock									$ 10	$ 13	$ 14