Note 6 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-based compensation expense	$ 145,321	$ 327,396	$ 385,605	$ 971,832
Research and Development Expense [Member]
Stock-based compensation expense	13,519	16,202	40,692	48,848
General and Administrative Expense [Member]
Stock-based compensation expense	$ 131,802	$ 311,194	$ 344,913	$ 922,984

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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