Note 4 - Net Income Per Share - Components of Diluted Shares (Details) - shares	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Weighted average common shares outstanding – basic (in shares)	4,833,604	4,833,232	4,833,356	4,834,324
Dilutive effect of stock options (in shares)	2,167	29	2,425	87
Shares used in computing net income per share – diluted (in shares)	4,835,770	4,833,261	4,835,781	4,834,411