Note 4 - Summary of Significant Accounting Policies - Weighted Average Number of Shares (Details) - shares	3 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Weighted average common shares outstanding – basic (in shares)	4,833,232	4,835,038
Dilutive effect of stock options (in shares)	3,589	119
Shares used in computing net income per share – diluted (in shares)	4,836,821	4,835,157