Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Basic (in shares)	4,833,232	4,846,010	4,834,324	4,846,010
Dilutive effect of stock options (in shares)	29	1,426	87	2,496
Shares used in computing net income per share – diluted (in shares)	4,833,261	4,847,436	4,834,411	4,848,506