Unaudited Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ 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
Net sales	$ 251,744	$ 265,943	$ 276,665	$ 286,947	$ 295,278	$ 289,745	$ 282,426	$ 293,196	$ 1,081,299	$ 1,160,645	$ 1,173,851
Gross margin	118,506	129,527	139,127	141,405	146,580	145,749	139,810	146,539	528,565	578,678	588,291
Operating income	33,219	22,669	41,244	40,891	46,155	39,621	36,030	40,622	138,023	162,428	$ 152,696
Net income	$ 27,685	$ 13,633	$ 33,553	$ 37,498	$ 36,613	$ 34,781	$ 29,227	$ 30,637	$ 112,369	$ 131,258
Class A Nonvoting Common Stock [Member]
Earnings (loss) from discontinued operations per Class A Common Share:
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