Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts receivable, allowance for doubtful accounts	$ 0	$ 0
Inventory, allowance for excess and obsolete inventory and lower of cost or estimated net realizable value adjustments	$ 185	$ 236
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	75,000,000
Common stock, shares issued (in shares)	44,615,000	41,782,000
Common stock, shares outstanding (in shares)	44,615,000	41,782,000