Quarterly Results of Operations (unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 233,371	$ 236,933	$ 288,498	$ 257,246	$ 239,476	$ 228,552	$ 224,538	$ 225,589	$ 1,016,048	$ 918,155	$ 871,922
Cost of sales	136,494	135,950	166,254	141,377	128,823	121,675	119,863	120,340	580,075	490,701	457,951
Gross profit	$ 96,877	$ 100,983	$ 122,244	$ 115,869	$ 110,653	$ 106,877	$ 104,675	$ 105,249	435,973	427,454	413,971
Gross profit percentage	41.50%	42.60%	42.40%	45.00%	46.20%	46.80%	46.60%	46.70%
Net income	$ (5,583)	$ 15,787	$ (2,263)	$ 5,767	$ 8,825	$ 8,175	$ 18,800	$ 19,242	$ 13,708	$ 55,042	$ 91,041
Earnings per common share:
Basic (in dollars per share)	$ (0.13)	$ 0.37	$ (0.05)	$ 0.14	$ 0.21	$ 0.20	$ 0.45	$ 0.46	$ 0.32	$ 1.32	$ 2.18
Diluted (in dollars per share)	$ (0.13)	$ 0.37	$ (0.05)	$ 0.14	$ 0.21	$ 0.20	$ 0.45	$ 0.46	$ 0.32	$ 1.32	$ 2.18