Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Basic (in shares)	4,835,038	4,846,010
Dilutive effect of stock options (in shares)	119	4,378
Shares used in computing net income per share – diluted (in shares)	4,835,157	4,850,388