Note 2 - Summary of Significant Accounting Policies - Weighted Average Number of Shares (Details) - shares	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Basic (in shares)	4,841,347	4,836,602	4,850,209
Dilutive effect of stock options (in shares)	4,865	1,787	2,393
Shares used in computing net income per share – diluted (in shares)	4,846,212	4,838,389	4,852,602