Note 9 - Stockholders' Equity - 2017 Liability Warrant Activity (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Outstanding as of January 1, 2017 (in shares) | shares	0
Outstanding as of January 1, 2017 (in dollars per share) | $ / shares	$ 0
Warrants granted (in shares) | shares	488,611
Warrants granted, exercise price (in dollars per share) | $ / shares	$ 11.25
Warrants exercised (in shares) | shares	(488,611)
Warrants exercised, , exercise price (in dollars per share) | $ / shares	$ 3.12
Outstanding as of December 31, 2017 (in shares) | shares	0
Outstanding as of December 31, 2017 (in dollars per share) | $ / shares	$ 0