Note 12 - Warrants - Summary of Warrant Activity (Details)	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Warrants outstanding (in shares) | shares	1,487,958
Warrants outstanding (in dollars per share) | $ / shares	$ 9.39
Warrants issued during the six months ended June 30, 2017 (see Note 9) (in shares) | shares	1,363,503
Warrants issued during the six months ended June 30, 2017 (see Note 9) (in dollars per share) | $ / shares	$ 2.80
Warrants outstanding (in dollars per share) | $ / shares	$ 21.22
Aggregate intrinsic value of outstanding warrants | $
Weighted average remaining contractual terms (Year)	4 years 94 days
Warrants exercised during the six months ended June 30, 2017 (see Note 9) (in shares) | shares	(2,251,606)
Warrants exercised during the six months ended June 30, 2017 (see Note 9) (in dollars per share) | $ / shares	$ 2.25
Warrants outstanding (in shares) | shares	599,855