Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Net sales									$ 261,162	$ 281,351	$ 284,188
Gross Profit on Sales	$ 23,725	$ 24,468	$ 23,960	$ 23,974	$ 25,181	$ 24,477	$ 22,229	$ 24,789	96,127	96,676
Net income	$ 9,008	$ 9,908	$ 7,879	$ 7,362	$ 10,074	$ 8,541	$ 5,273	$ 8,823	$ 34,157	$ 32,711	$ 43,143
Net income available to common shareholders, per common and common equivalent share:
Basic	$ 0.95	$ 1.05	$ 0.83	$ 0.78	$ 1.07	$ 0.91	$ 0.56	$ 0.94	$ 3.62	$ 3.48	$ 4.60
Diluted	$ 0.95	$ 1.04	$ 0.83	$ 0.77	$ 1.07	$ 0.90	$ 0.56	$ 0.93	$ 3.59	$ 3.46	$ 4.56
Product
Net sales	$ 63,202	$ 64,157	$ 64,626	$ 65,757	$ 69,150	$ 70,883	$ 65,442	$ 71,364	$ 257,742	$ 276,839	$ 278,962