Earnings Per Share (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
Numerator:
Net income	$ 23,487	$ (166)	$ 9,786	$ 12,062	$ 12,270	$ 16,646	$ 10,159	$ 22,189	$ 45,169	$ 61,264	$ 75,544
Denominator:
Denominator for basic earnings per common share-weighted average shares (shares)									25,970,000	25,965,000	25,800,000
Effect of dilutive securities:
Employee and Director stock awards (shares)									66,000	132,000	137,000
Denominator for diluted earnings per common share (shares)									26,036,000	26,097,000	25,937,000
Earnings per share basic and diluted:
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