Note 16 - Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax at federal statutory rate	$ (4,185,000)	$ (3,505,000)	$ (2,277,000)
State, net of federal benefit	(1,238,000)	(315,000)	(335,000)
Research and development credit	(135,000)	(89,000)	(51,000)
Stock-based compensation	344,000	136,000	89,000
Nondeductible interest		590,000	471,000
Warrant and derivative revaluation		328,000	(589,000)
Change in Federal tax rate	8,172,000
Other	7,000	94,000	5,000
Change in valuation allowance	(2,965,000)	2,761,000	2,687,000
Total provision for income taxes	$ 0	$ 0	$ 0