Quarterly Results of Operations (unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Quarterly Results of Operations (unaudited)
Net sales	$ 179,002,000	$ 173,703,000	$ 158,271,000	$ 153,779,000	$ 151,255,000	$ 141,508,000	$ 135,430,000	$ 136,811,000	$ 664,755,000	$ 565,004,000	$ 488,749,000
Cost of sales	93,672,000	93,382,000	85,934,000	82,581,000	82,492,000	77,909,000	74,839,000	76,297,000	355,569,000	311,537,000	275,450,000
Gross profit	$ 85,330,000	$ 80,321,000	$ 72,337,000	$ 71,198,000	$ 68,763,000	$ 63,599,000	$ 60,591,000	$ 60,514,000	309,186,000	253,467,000	213,299,000
Gross profit percentage	47.70%	46.20%	45.70%	46.30%	45.50%	44.90%	44.70%	44.20%
Net income	$ 16,291,000	$ 14,019,000	$ 15,389,000	$ 14,254,000	$ 13,273,000	$ 12,356,000	$ 11,085,000	$ 11,239,000	$ 59,953,000	$ 47,953,000	$ 43,265,000
Earnings per common share:
Basic (in dollars per share)	$ 0.39	$ 0.34	$ 0.37	$ 0.34	$ 0.32	$ 0.30	$ 0.27	$ 0.27	$ 1.44	$ 1.16	$ 1.05
Diluted (in dollars per share)	$ 0.39	$ 0.34	$ 0.37	$ 0.34	$ 0.32	$ 0.30	$ 0.27	$ 0.27	$ 1.44	$ 1.15	$ 1.04