Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	[1]
Accounts receivable, allowance for doubtful accounts	$ 469	$ 284
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	46,574,958	46,363,945
Common stock, shares outstanding (in shares)	46,574,958	46,363,945

[1] The condensed consolidated balance sheet as of December 31, 2018 has been derived from the audited consolidated financial statements as of that date.