Note 12 - Stockholders' Equity - Outstanding Warrants (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Outstanding warrants (in shares)	544	544	565
Outstanding warrants, weighted-average exercise price (in dollars per share)	$ 1.81	$ 1.81	$ 1.81
Warrants granted (in shares)	8,438
Warrants granted, weighted average exercise price (in dollars per share)	$ 1.11
Warrants exercised (in shares)	(394)		(21)
Warrants exercised, weighted average exercise price (in dollars per share)	$ 0.21		$ 1.81
Warrants expired (in shares)
Warrants expired, weighted average exercise price (in dollars per share)
Warrants exercised (in shares)	394		21
Warrants expired (in shares)
Outstanding warrants (in shares)	8,588	544	544
Outstanding warrants, weighted-average exercise price (in dollars per share)	$ 1.09	$ 1.81	$ 1.81