Note 4 - Net Income Per Share - Components of Common Shares Outstanding (Details) - shares	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Weighted average common shares outstanding – basic (in shares)	4,841,010	4,835,010
Dilutive effect of stock options (in shares)	5,241	2,085
Shares used in computing net income per share – diluted (in shares)	4,846,251	4,837,095