Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Net sales									$ 281,351	$ 284,188	$ 252,560
Gross Profit on Sales	$ 25,181	$ 24,477	$ 22,229	$ 24,789	$ 27,999	$ 29,401	$ 22,744	$ 23,682	96,676	103,826
Net income	$ 10,074	$ 8,541	$ 5,273	$ 8,823	$ 11,163	$ 13,543	$ 10,122	$ 8,315	$ 32,711	$ 43,143	$ 42,014
Net income available to common shareholders, per common and common equivalent share
Basic	$ 1.07	$ 0.91	$ 0.56	$ 0.94	$ 1.19	$ 1.44	$ 1.08	$ 0.89	$ 3.48	$ 4.60	$ 4.49
Diluted	$ 1.07	$ 0.90	$ 0.56	$ 0.93	$ 1.18	$ 1.43	$ 1.07	$ 0.88	$ 3.46	$ 4.56	$ 4.44
Product
Net sales	$ 69,150	$ 70,883	$ 65,442	$ 71,364	$ 75,997	$ 77,653	$ 64,735	$ 60,577	$ 276,839	$ 278,962	$ 247,877