Condensed Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 232	$ 260
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	44,923	45,671
Preferred stock, shares outstanding (in shares)	44,923	45,671
Preferred stock, liquidation value	$ 45,640	$ 44,718
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	60,052,992	34,921,999
Common stock, shares outstanding (in shares)	60,052,992	34,921,999