Unaudited Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Net sales	$ 295,278	$ 289,745	$ 282,426	$ 293,196	$ 297,499	$ 298,421	$ 287,780	$ 290,151	$ 1,160,645	$ 1,173,851	$ 1,113,316
Gross margin	146,580	145,749	139,810	146,539	147,452	151,082	143,692	146,065	578,678	588,291	558,292
Operating income	46,155	39,621	36,030	40,622	44,780	37,709	34,796	35,411	162,428	152,696	131,015
Net income	$ 36,613	$ 34,781	$ 29,227	$ 30,637	$ 34,951	$ 26,000	$ 4,273	$ 25,836	$ 131,258	$ 91,060	$ 95,645
Class A Nonvoting Common Stock [Member]
Earnings (loss) from discontinued operations per Class A Common Share:
Net income per share, basic	$ 0.69	$ 0.66	$ 0.56	$ 0.59	$ 0.67	$ 0.50	$ 0.08	$ 0.50	$ 2.50	$ 1.76	$ 1.87
Net income per share, diluted	$ 0.68	$ 0.65	$ 0.55	$ 0.58	$ 0.66	$ 0.49	$ 0.08	$ 0.49	$ 2.46	$ 1.73	$ 1.84