Acquisitions - Pro Forma Operating Results (Details) - USD ($) $ / shares in Units, $ 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
Business Acquisition [Line Items]
Net sales	$ 297,499	$ 298,421	$ 287,780	$ 290,151	$ 289,212	$ 275,927	$ 268,001	$ 280,176	$ 1,173,851	$ 1,113,316	$ 1,120,625
(Loss) earnings from continuing operations, as reported	$ 34,951	$ 26,000	$ 4,273	$ 25,836	$ 25,242	$ 22,553	$ 25,297	$ 22,553	$ 91,060	$ 95,645	$ 80,110
Nonvoting Common Stock [Member]
Business Acquisition [Line Items]
Basic (loss) earnings from continuing operations per Class A Common Share, as reported	$ 0.67	$ 0.50	$ 0.08	$ 0.50	$ 0.49	$ 0.44	$ 0.50	$ 0.45	$ 1.76	$ 1.87
Diluted (loss) earnings from continuing operations per Class A Common Share, as reported	$ 0.66	$ 0.49	$ 0.08	$ 0.49	$ 0.48	$ 0.43	$ 0.49	$ 0.44	$ 1.73	$ 1.84