Note 15 - Selected Quarterly Financial Data (Unaudited) - Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Mar. 31, 2018	[1]	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Net sales	$ 8,101		$ 9,150		$ 8,055		$ 8,809		$ 7,253		$ 7,605		$ 9,862		$ 7,322		$ 34,115	$ 32,042	$ 31,840
Gross profit	1,908		4,240		3,620		3,603		2,661		2,857		3,885		2,821		13,371	12,224	11,866
Net income (loss)	$ (1,058)		$ 1,107		$ 475		$ 501		$ (274)		$ (349)		$ 99		$ (691)		$ 1,025	$ (1,215)	$ (4,395)
Net income (loss) per share
Basic and diluted loss per share (in dollars per share)	$ (0.18)		$ 0.19		$ 0.08		$ 0.09		$ (0.05)		$ (0.06)		$ 0.02		$ (0.12)		$ 0.18	$ (0.21)	$ (0.79)
Net sales	$ 8,101		$ 9,150		$ 8,055		$ 8,809		$ 7,253		$ 7,605		$ 9,862		$ 7,322		$ 34,115	$ 32,042	$ 31,840
Gross profit	1,908		4,240		3,620		3,603		2,661		2,857		3,885		2,821		13,371	12,224	11,866
Net income (loss)	$ (1,058)		$ 1,107		$ 475		$ 501		$ (274)		$ (349)		$ 99		$ (691)		$ 1,025	$ (1,215)	$ (4,395)

[1] The first, second, third and fourth quarters of 2018 include abnormal production costs of $9,000, $75,000, $4,000 and $720,000, respectively. The first, second, third and fourth quarters of 2017 include abnormal production costs of $28,000, $73,000, $148,000 and $5,000, respectively.