Note 12 - Stockholders' Equity - Outstanding Warrants (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Outstanding warrants (in shares) | shares	8,588
Outstanding warrants, weighted-average exercise price (in dollars per share) | $ / shares	$ 1.09
Warrants granted (in shares) | shares
Warrants granted, weighted average exercise price (in dollars per share) | $ / shares
Warrants exercised (in shares) | shares	(299)
Warrants exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 0.71
Warrants expired (in shares) | shares	(42)
Warrants expired, weighted average exercise price (in dollars per share) | $ / shares	$ 0.21
Outstanding warrants (in shares) | shares	8,247
Outstanding warrants, weighted-average exercise price (in dollars per share) | $ / shares	$ 1.11