Condensed Balance Sheets (Current Period Unaudited) (Parentheticals) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Preferred stock, shares authorized (in shares)	10,000,000
Preferred stock, shares issued (in shares)	9,577
Preferred stock, shares outstanding (in shares)	3,337	3,337
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	27,976,823	26,455,352
Common stock, shares outstanding (in shares)	27,976,823	26,455,352
Series A Convertible Preferred Stock [Member]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	9,578	0
Preferred stock, shares issued (in shares)	9,577	0
Preferred stock, shares outstanding (in shares)	3,337	0
Undesignated Preferred Stock [Member]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	9,990,422	9,990,422
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0