Note 6 - Stock-based Compensation - Summary of Stock Options and Warrants (Details) - $ / shares	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Option Shares Reserved [Member]
Options Outstanding (in shares)	143,230	147,230	151,230	155,230
Granted (in shares)	(4,000)	(4,000)	(4,000)
Granted (in shares)	4,000	4,000	4,000
Exercised (in shares)
Terminated (in shares)
Employee Stock Option [Member]
Options Outstanding (in shares)	19,000	21,000	35,090	38,000
Weighted Average Option Exercise Price (in dollars per share)	$ 57.51	$ 52.85	$ 33.51	$ 31.78
Granted (in shares)	(4,000)	(4,000)	(4,000)
Granted (in shares)	4,000	4,000	4,000
Granted (in dollars per share)	$ 57.46	$ 56.76	$ 67.69
Exercised (in shares)	(6,000)	(18,090)	(6,910)
Exercised (in dollars per share)	$ 41.19	$ 16.19	$ 43.81
Terminated (in shares)
Terminated (in dollars per share)
Warrants [Member]
Options Outstanding (in shares)	0	0	0	2,000
Weighted Average Option Exercise Price (in dollars per share)				$ 37.38
Granted (in shares)
Granted (in shares)
Granted (in dollars per share)
Exercised (in shares)
Exercised (in dollars per share)
Terminated (in shares)			(2,000)
Terminated (in dollars per share)			$ 37.38