Note 4 - Components of Common Shares Outstanding (Details) - shares	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Weighted average common shares outstanding – basic (in shares)	4,835,564	4,855,398	4,835,289	4,858,557
Dilutive effect of stock options (in shares)	2,255	2,735	2,004	3,874
Shares used in computing net income per share – diluted (in shares)	4,837,819	4,858,133	4,837,293	4,862,431