Note 9 - Convertible Promissory Notes, Related Parties (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Feb. 13, 2018	Dec. 10, 2014	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest Expense, Total					$ 315	$ 821
Debt Conversion, Converted Instrument, Amount						35,577
Other Ownership Interests, Contributed Capital	$ 21,400
Convertible Promissory Notes Issued in 2014 and 2015 [Member]
Debt Instrument, Interest Rate, Stated Percentage			8.00%
Long-term Debt, Gross	35,600						$ 35,300
Debt Instrument, Principal Amount	29,400						29,400
Debt Instrument, Interest Amount	6,600						6,300
Debt Instrument, Unamortized Discount, Total	$ 400						$ 400
Interest Expense, Total						$ 300
Debt Conversion, Converted Instrument, Shares Issued (in shares)	1,571,702
Debt Instrument, Convertible, Conversion Price (in dollars per share)	$ 9.05
Debt Conversion, Converted Instrument, Amount	$ 14,200
Note Purchase Agreement [Member]
Proceeds from Convertible Debt		$ 18,400
Second Note Purchase Agreement [Member]
Proceeds from Convertible Debt			$ 11,000