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, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Earnings Per Share [Line Items]
Net earnings	$ 29,227	$ 4,273	$ 59,864	$ 30,109
Denominator for basic earnings per share for both Class A and Class B	52,532	51,698	52,366	51,569
Plus: Effect of dilutive stock options	674	1,021	716	982
Denominator for diluted earnings per share for both Class A and Class B	53,206	52,719	53,082	52,551
Class A nonvoting common stock
Earnings Per Share [Line Items]
Net earnings per share, basic	$ 0.56	$ 0.08	$ 1.14	$ 0.58
Net earnings per share, diluted	$ 0.55	$ 0.08	$ 1.13	$ 0.57
Class B voting common stock
Earnings Per Share [Line Items]
Preferential dividends	$ 0	$ 0	$ 815	$ 799
Preferential dividends on dilutive stock options	0	0	13	(16)
Numerator for basic and diluted earnings per Class B Voting Common Share	$ 29,227	$ 4,273	$ 59,036	$ 29,294
Net earnings per share, basic	$ 0.56	$ 0.08	$ 1.13	$ 0.57
Net earnings per share, diluted	$ 0.55	$ 0.08	$ 1.11	$ 0.56