Note 4 - Summary of Significant Accounting Policies - Weighted Average Number of Shares (Details) - shares	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Weighted average common shares outstanding – basic (in shares)	4,833,232	4,834,709	4,833,232	4,834,872
Dilutive effect of stock options (in shares)	3,371	100	3,389	114
Shares used in computing net income per share – diluted (in shares)	4,836,603	4,834,809	4,836,621	4,834,986