Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Weighted average common shares outstanding – basic (in shares)	4,841,369	4,836,336	4,841,130	4,835,639
Dilutive effect of stock options (in shares)	5,921	3,441	4,906	2,176
Shares used in computing net income per share – diluted (in shares)	4,847,290	4,839,777	4,846,036	4,837,815