Note 13 - Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax at federal statutory rate	$ (3,089,000)	$ (2,937,000)	$ (4,185,000)
State, net of federal benefit	(414,000)	(455,000)	(1,238,000)
Research and development credit	(225,000)	(236,000)	(135,000)
Stock-based compensation	446,000	440,000	344,000
Change in Federal Tax Rate			8,172,000
Other	5,000	22,000	7,000
Change in valuation allowance	3,277,000	3,166,000	(2,965,000)
Total provision for income taxes	$ 0	$ 0	$ 0