Note 8 - Net Loss Per Share - Schedule of Earnings Per Share (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Net loss	$ (3,285,914)	$ (7,262,529)	$ (4,073,307)	$ (3,309,866)	$ (4,142,577)	$ (1,874,382)	$ (14,621,750)	$ (9,326,825)
Deemed dividend attributable to preferred stock								(11,479,308)
Net loss attributable to common shareholders	$ (3,285,914)			$ (3,309,866)			$ (14,621,750)	$ (20,806,133)
Weighted average common shares outstanding used to compute net loss per share, basic and diluted (in shares)	9,130,057			5,183,492			8,283,302	3,645,682
Net loss per share of common stock, basic and diluted: (in dollars per share)	$ (0.36)			$ (0.64)			$ (1.77)	$ (5.71)