Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Weighted average common shares outstanding – basic (in shares)	4,846,010	4,845,010	4,846,010	4,843,355
Dilutive effect of stock options (in shares)	1,426	5,497	2,496	6,765
Shares used in computing net income per share – diluted (in shares)	4,847,436	4,850,507	4,848,506	4,850,120