Note 8 - Stock-based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allocated Share-based Compensation Expense	$ 315,066	$ 338,162	$ 681,449	$ 731,633
Research and Development Expense [Member]
Allocated Share-based Compensation Expense	24,072	184,051	67,404	426,328
General and Administrative Expense [Member]
Allocated Share-based Compensation Expense	$ 290,994	$ 154,111	$ 614,045	$ 305,305