Unaudited Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Jul. 31, 2017		Apr. 30, 2017		Jan. 31, 2017		Oct. 31, 2016		Jul. 31, 2016		Apr. 30, 2016		Jan. 31, 2016		Oct. 31, 2015		Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Net sales	$ 289,212		$ 275,927		$ 268,001		$ 280,176		$ 282,106		$ 286,816		$ 268,630		$ 283,073		$ 1,113,316	$ 1,120,625	$ 1,171,731
Gross margin	143,867		139,909		134,158		140,358		141,089		145,443		132,892		139,349		558,292	558,773	558,432
Operating income	36,295	[1]	31,550	[1]	29,962	[1]	33,208	[1]	33,403	[1]	30,784	[1]	23,589	[1]	30,102	[1]	131,015	117,878	35,306
Net earnings	$ 25,242		$ 22,553		$ 25,297		$ 22,553		$ 25,136		$ 20,981		$ 15,290		$ 18,703		95,645	80,110	4,902
(Loss) earnings from discontinued operations, net of income taxes																	$ 0	$ 0	$ (1,915)
Class A Nonvoting Common Stock [Member]
Net earnings (loss) from continuing operations per Class A Common Share:
Earnings (loss) from continuing operations, per basic share	$ 0.49	[2]	$ 0.44	[2]	$ 0.50	[2]	$ 0.45	[2]	$ 0.50	[2]	$ 0.42	[2]	$ 0.30	[2]	$ 0.37	[2]	$ 1.87	$ 1.59	$ 0.10
Diluted (loss) earnings from continuing operations per Class A Common Share, as reported	$ 0.48	[2]	$ 0.43	[2]	$ 0.49	[2]	$ 0.44	[2]	$ 0.49	[2]	$ 0.42	[2]	$ 0.30	[2]	$ 0.37	[2]	1.84	1.58	0.10
Earnings (loss) from discontinued operations per Class A Common Share:
Basic (in dollars per share)																	0.00	0.00	(0.04)
Diluted (in dollars per share)																	$ 0.00	$ 0.00	$ (0.04)

[1] Quarters First Second Third Fourth TotalFiscal 2016 Net sales $283,073 $268,630 $286,816 $282,106 $1,120,625Gross margin 139,349 132,892 145,443 141,089 558,773Operating income 30,102 23,589 30,784 33,403 117,878Net earnings 18,703 15,290 20,981 25,136 80,110Net earnings per Class A Nonvoting Common Share: Basic $0.37 $0.30 $0.42 $0.50 $1.59Diluted $0.37 $0.30 $0.42 $0.49 $1.58Fiscal 2017 Net sales $280,176 $268,001 $275,927 $289,212 $1,113,316Gross margin 140,358 134,158 139,909 143,867 558,292Operating income 33,208 29,962 31,550 36,295 131,015Net earnings 22,553 25,297 22,553 25,242 95,645Net earnings per Class A Nonvoting Common Share: Basic * $0.45 $0.50 $0.44 $0.49 $1.87Diluted $0.44 $0.49 $0.43 $0.48 $1.84

[2] Quarters First Second Third Fourth TotalFiscal 2016 Net sales $283,073 $268,630 $286,816 $282,106 $1,120,625Gross margin 139,349 132,892 145,443 141,089 558,773Operating income 30,102 23,589 30,784 33,403 117,878Net earnings 18,703 15,290 20,981 25,136 80,110Net earnings per Class A Nonvoting Common Share: Basic $0.37 $0.30 $0.42 $0.50 $1.59Diluted $0.37 $0.30 $0.42 $0.49 $1.58Fiscal 2017 Net sales $280,176 $268,001 $275,927 $289,212 $1,113,316Gross margin 140,358 134,158 139,909 143,867 558,292Operating income 33,208 29,962 31,550 36,295 131,015Net earnings 22,553 25,297 22,553 25,242 95,645Net earnings per Class A Nonvoting Common Share: Basic * $0.45 $0.50 $0.44 $0.49 $1.87Diluted $0.44 $0.49 $0.43 $0.48 $1.84* The sum of the quarters does not equal the year-to-date total for fiscal 2017 due to the quarterly changes in weighted-average shares outstanding.