Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended		6 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Basic (in shares)	4,830,826	4,833,232	4,830,826	4,833,232
Dilutive effect of stock options (in shares)	130	3,371	101	3,389
Shares used in computing net income per share – diluted (in shares)	4,830,956	4,836,603	4,830,927	4,836,621
Weighted average common shares outstanding – basic (in shares)	4,830,826	4,833,232	4,830,826	4,833,232
Dilutive effect of stock options (in shares)	130	3,371	101	3,389