Note 8 - Common Stock (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2019

Dec. 31, 2018

Notes Tables

Common Stock Reserved for Future Issuance [Table Text Block]

	September 30,		December 31,
	2019		2018
Conversion of Series A Preferred Stock		21,771,032		22,112,775
Stock-based compensation awards		6,818,214		5,163,957
Employee Stock Purchase Plan		118,120		118,120
Total		28,707,366		27,394,852

	December 31,		December 31,
	2018		2017
Conversion of Series A Preferred Stock		22,112,775		22,112,775
Stock-based compensation awards		5,163,957		3,572,457
Employee Stock Purchase Plan		118,120		192,463
Total		27,394,852		25,877,695