Note 3 - Valuation and Qualifying Accounts - Activity in the Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Balance at beginning of period	$ 35	$ 27	$ 13
Bad debt expense	85	112	421
Write-off of uncollectible accounts receivable	(81)	(104)	(407)
Balance at end of year	$ 39	$ 35	$ 27