Note 9 - Common Stock (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

					Number of
					Shares
					Outstanding
	Exercisable	Expiration	Exercise		Under
Issuance Date	for	Date	Price		Warrants
September 2014	Common Shares	September 23, 2019	$	4.24		86,831
October 2014	Common Shares	October 13, 2019	$	4.24		29,000
November 2014	Common Shares	November 12, 2019	$	4.24		12,500
February 2015	Common Shares	February 17, 2025	$	4.00		75,697
March 2015	Common Shares	March 26, 2025	$	2.72		1,454
May 2015	Common Shares	May 12, 2025	$	4.24		36,229
May 2015	Common Shares	May 17, 2020	$	4.24		21,585
December 2015	Common Shares	December 16, 2025	$	5.60		26,875
April 2016	Common Shares	April 1, 2026	$	6.08		25,000
May 2016	Common Shares	May 11, 2021	$	7.74		5,000
June 2016	Common Shares	June 20, 2026	$	4.98		100,402
May 2017	Common Shares	May 25, 2027	$	9.50		222,049
						642,622