Note 16 - Quarterly Financial Information (Unaudited) - Financial Statement Reclassification (Details) (Parentheticals) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Accounts receivable, allowance for doubtful accounts	$ 68	$ 68	$ 26	$ 0	$ 0	$ 0	$ 0	$ 6
Preferred stock, par value (in dollars per share)		$ 0.001	$ 0.001	$ 0.001		$ 0.001	$ 0.001	$ 0.001
Preferred stock, authorized (in shares)		1,000,000	1,000,000	1,000,000		1,000,000	1,000,000	1,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Common stock, authorized (in shares)	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000
Common stock, issued (in shares)	20,825,452	20,344,825	18,898,609	18,717,095	18,547,406	18,237,425	16,107,505	14,145,413
Common stock, outstanding (in shares)	20,825,452	20,344,825	18,898,609	18,717,095	18,547,406	18,237,425	16,107,505	14,145,413
Series A Preferred Stock [Member]
Preferred stock, designated (in shares)		4,250	4,250	4,250		4,250	4,250	4,250
Preferred stock, issued (in shares)		0	0	0		4,250	4,250	4,250
Preferred stock, outstanding (in shares)		0	0	0		4,250	4,250	4,250