Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Weighted average common shares outstanding – basic (in shares)	4,836,336	4,844,845	4,835,639	4,853,970
Dilutive effect of stock options (in shares)	3,441	2,125	2,176	3,133
Shares used in computing net income per share – diluted (in shares)	4,839,777	4,846,970	4,837,815	4,857,103