Quarterly Results of Operations (unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 239,476	$ 228,552	$ 224,538	$ 225,589	$ 228,854	$ 217,268	$ 213,034	$ 212,766	$ 918,155	$ 871,922	$ 770,157
Cost of sales	128,823	121,675	119,863	120,340	121,451	112,594	111,799	112,107	490,701	457,951	402,997
Gross profit	$ 110,653	$ 106,877	$ 104,675	$ 105,249	$ 107,403	$ 104,674	$ 101,235	$ 100,659	427,454	413,971	367,160
Gross profit percentage	46.20%	46.80%	46.60%	46.70%	46.90%	48.20%	47.50%	47.30%
Net income	$ 8,825	$ 8,175	$ 18,800	$ 19,242	$ 16,888	$ 18,736	$ 32,488	$ 22,929	$ 55,042	$ 91,041	$ 71,378
Earnings per common share:
Basic (in dollars per share)	$ 0.21	$ 0.20	$ 0.45	$ 0.46	$ 0.41	$ 0.45	$ 0.78	$ 0.55	$ 1.32	$ 2.18	$ 1.71
Diluted (in dollars per share)	$ 0.21	$ 0.20	$ 0.45	$ 0.46	$ 0.41	$ 0.45	$ 0.78	$ 0.55	$ 1.32	$ 2.18	$ 1.71