Note 18 - Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Net sales	$ 8,634	$ 7,504	$ 7,690	$ 8,071	$ 6,059	$ 10,044	$ 6,954	$ 7,145	$ 31,899	$ 30,202
Gross profit	3,084	2,877	3,063	3,676	2,229	4,116	2,285	1,836	12,700	10,466	$ 13,371
Net income (loss)	$ 121	$ 171	$ 228	$ (133)	$ (1,473)	$ 288	$ (1,136)	$ (1,275)	$ 387	$ (3,596)	$ 1,025
Basic and diluted loss per share (in dollars per share)	$ 0.01	$ 0.03	$ 0.04	$ (0.02)	$ (0.25)	$ 0.05	$ (0.20)	$ (0.22)	$ 0.06	$ (0.62)