Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - $ / shares	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 02, 2017
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000	10,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000	100,000,000
Common stock, shares issued (in shares)	19,585,394	19,243,651	17,674,729
Common stock, shares outstanding (in shares)	19,585,394	19,243,651	17,674,729
Series A Convertible Preferred Stock [Member]
Preferred stock, par value (in dollars per share)		$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	22,000	22,000	22,000
Preferred stock, shares issued (in shares)	21,660	22,000	22,000
Preferred stock, shares outstanding (in shares)	21,660	22,000	22,000

Face amount or stated value per share of common stock.

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