Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2021	Oct. 31, 2020	Oct. 31, 2021	Oct. 31, 2020
Net income per common share:
Net income	$ 2,792	$ 9,264	$ 9,991	$ 27,237
Denominator for basic net income per share (weighted-average shares which exclude shares in the treasury, 509,242 at April 30, 2021 and 2020	7,849,591	7,979,902	7,942,162	7,976,228
Effect of dilutive securities from restricted stock plan	149,374	143,946	152,863	134,207
Denominator for diluted net income per share (adjusted weighted average shares)	7,998,965	8,123,848	8,095,025	8,110,435
Basic net income per share	$ 0.36	$ 1.16	$ 1.26	$ 3.41
Diluted net income per share	$ 0.35	$ 1.14	$ 1.23	$ 3.36