Quarterly Results of Operations (unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2013
Quarterly Results of Operations (unaudited)
Net sales	$ 151,255,000	$ 141,508,000	$ 135,430,000	$ 136,811,000	$ 131,377,000	$ 120,058,000	$ 119,042,000	$ 118,272,000	$ 565,004,000	$ 488,749,000	$ 425,026,000
Cost of sales	82,492,000	77,909,000	74,839,000	76,297,000	74,330,000	67,640,000	66,707,000	66,773,000	311,537,000	275,450,000	241,550,000
Gross profit	$ 68,763,000	$ 63,599,000	$ 60,591,000	$ 60,514,000	$ 57,047,000	$ 52,418,000	$ 52,335,000	$ 51,499,000	253,467,000	213,299,000	183,476,000
Gross profit percentage	45.50%	44.90%	44.70%	44.20%	43.40%	43.70%	44.00%	43.50%
Net income	$ 13,273,000	$ 12,356,000	$ 11,085,000	$ 11,239,000	$ 10,705,000	$ 10,249,000	$ 11,126,000	$ 11,185,000	$ 47,953,000	$ 43,265,000	$ 39,239,000
Earnings per common share:
Basic (in dollars per share)	$ 0.32	$ 0.30	$ 0.27	$ 0.27	$ 0.26	$ 0.25	$ 0.27	$ 0.27	$ 1.16	$ 1.05	$ 0.96
Diluted (in dollars per share)	$ 0.32	$ 0.30	$ 0.27	$ 0.27	$ 0.26	$ 0.25	$ 0.27	$ 0.27	$ 1.15	$ 1.04	$ 0.95