Consolidated Balance Sheets (Parentheticals) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Preferred stock, shares authorized (in shares)	5,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001
Common stock, shares authorized (in shares)	170,000,000	170,000,000
Common stock, shares issued (in shares)	13,972,158	7,691,324
Common stock, shares outstanding (in shares)	13,972,158	7,691,324
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Series A-1 Convertible Preferred Stock [Member]
Preferred stock, shares authorized (in shares)	100,000	100,000
Preferred stock, liquidation value	$ 100	$ 100
Preferred stock, shares issued (in shares)	0	62,596
Preferred stock, shares outstanding (in shares)	0	62,596
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Series B-1 Convertible Preferred Stock [Member]
Preferred stock, shares authorized (in shares)	105,000	105,000
Preferred stock, liquidation value	$ 100	$ 100
Preferred stock, shares issued (in shares)	0	105,000
Preferred stock, shares outstanding (in shares)	0	105,000
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001