Note 8 - Net Loss Per Share - Schedule of Earnings Per Share (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Net loss	$ (7,262,529)	$ (4,073,307)	$ (4,142,577)	$ (1,874,382)	$ (11,335,836)	$ (6,016,959)
Deemed dividend attributable to preferred stock			(11,479,308)			(11,479,308)
Net loss attributable to common shareholders	$ (7,262,529)		$ (15,621,885)		$ (11,335,836)	$ (17,496,267)
Net loss per share of common stock, basic and diluted: (in dollars per share)	$ (0.80)		$ (5.08)		$ (1.44)	$ (6.11)