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, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Line Items]
Earnings from continuing operations	$ 34,951	$ 26,000	$ 4,273	$ 25,836	$ 25,242	$ 22,553	$ 25,297	$ 22,553	$ 91,060	$ 95,645	$ 80,110
Cash dividends on Common Stock									$ 42,873	$ 41,880	$ 40,808
Denominator for basic earnings per share for both Class A and Class B									51,677	51,056	50,541
Plus: Effect of dilutive stock options									847	900	228
Denominator for diluted earnings per share for both Class A and Class B									52,524	51,956	50,769
Class A Nonvoting Common Stock [Member]
Earnings Per Share [Line Items]
Earnings (loss) from continuing operations, per basic share	$ 0.67	$ 0.50	$ 0.08	$ 0.50	$ 0.49	$ 0.44	$ 0.50	$ 0.45	$ 1.76	$ 1.87
Earnings (loss) from continuing operations, per diluted share	$ 0.66	$ 0.49	$ 0.08	$ 0.49	$ 0.48	$ 0.43	$ 0.49	$ 0.44	1.73	1.84
Net earnings (loss) per share, basic									1.76	1.87	$ 1.59
Net earnings (loss) per share, diluted									$ 1.73	$ 1.84	$ 1.58
Class B Voting Common Stock [Member]
Earnings Per Share [Line Items]
Earnings from continuing operations									$ 90,247	$ 94,843	$ 79,326
Net earnings (loss) per share, basic									$ 1.75	$ 1.86	$ 1.57
Net earnings (loss) per share, diluted									$ 1.72	$ 1.83	$ 1.56
Preferential Dividends on Class A Nonvoting Common Stock [Member]
Earnings Per Share [Line Items]
Cash dividends on Common Stock									$ 799	$ 788	$ 783
Preferential Dividends on Dilutive Shares [Member]
Earnings Per Share [Line Items]
Cash dividends on Common Stock									$ 14	$ 14	$ 1