Quarterly Financial Information, Unaudited (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 28, 2018	Feb. 28, 2017	Feb. 29, 2016
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 200,660	$ 208,158	$ 196,329	$ 205,283	$ 184,266	$ 228,116	$ 200,790	$ 250,366	$ 810,430	$ 863,538	$ 889,400
Gross profit	38,010	31,117	43,800	47,382	46,803	51,297	42,104	65,128	160,309	205,332	228,118
Net income	$ 23,487	$ (166)	$ 9,786	$ 12,062	$ 12,270	$ 16,646	$ 10,159	$ 22,189	$ 45,169	$ 61,264	$ 75,544
Basic earnings per common share (usd per share)	$ 0.91	$ (0.01)	$ 0.38	$ 0.46	$ 0.47	$ 0.64	$ 0.39	$ 0.86	$ 1.74	$ 2.36	$ 2.93
Diluted earnings per common share (usd per share)	$ 0.90	$ (0.01)	$ 0.38	$ 0.46	$ 0.47	$ 0.64	$ 0.39	$ 0.85	$ 1.73	$ 2.35	$ 2.91