Unaudited Quarterly Financial Data (Details) - USD ($)	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, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018
Selected Quarterly Financial Information [Abstract]
Net sales	$ 149,673,000	$ 135,121,000	$ 161,654,000	$ 170,267,000	$ 176,372,000	$ 170,448,000	$ 164,133,000	$ 160,844,000	$ 167,435,000	$ 147,854,000	$ 133,731,000	$ 121,569,000	$ 616,715,000	$ 671,797,000	$ 570,589,000
Gross profit	49,663,000	53,001,000	60,602,000	63,567,000	64,010,000	64,416,000	61,245,000	57,769,000	62,988,000	62,436,000	50,801,000	47,716,000	226,833,000	247,440,000	223,941,000
Net income	$ 1,126,000	$ (3,989,000)	$ 3,495,000	$ 6,388,000	$ 6,135,000	$ 7,612,000	$ 7,826,000	$ 3,468,000	$ 7,458,000	$ 8,210,000	$ 15,761,000	$ (1,660,000)	$ 7,020,000	$ 25,041,000	$ 29,769,000
Diluted income (loss) per share (in dollars per share)	$ 0.04	$ (0.16)	$ 0.14	$ 0.26	$ 0.25	$ 0.31	$ 0.32	$ 0.14	$ 0.31	$ 0.34	$ 0.66	$ (0.07)	$ 0.28	$ 1.03	$ 1.24