Note 10 - Summary of Stock Options (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Six Months Ended June 30, 2019
						Weighted
				Weighted		Average
	Number			Average		Remaining		Aggregate
	of			Exercise		Contractual		Intrinsic
	Shares			Price		Term (years)		Value
Options outstanding, beginning of period		4,014,475		$	4.56		7.4	$	-
Options granted		2,335,000		$	1.18
Options exercised		-
Options canceled		(1,035,100	)	$	4.94
Options outstanding, end of period		5,314,375		$	3.00		8.6	$	-
Vested and exercisable and expected to vest, end of period		5,054,030		$	3.04		8.6	$	-
Vested and exercisable, end of period		1,790,963		$	4.26		7.6	$	-

Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block]

							Weighted
			Number		Weighted		Average		Number		Weighted
			Outstanding		Average		Remaining		Exercisable		Average
Range of			as of		Exercise		Contractual		as of		Exercise
Exercise Prices			June 30, 2019		Price		Term (Years)		June 30, 2019		Price
$0.38	-	$0.58		190,000	$	0.53		9.93		-	$	-
$1.00	-	$1.97		2,643,195	$	1.38		9.42		485,265	$	1.52
$2.02	-	$2.83		85,000	$	2.48		8.62		20,520	$	2.65
$3.03	-	$3.82		474,376	$	3.55		8.55		175,002	$	3.65
$4.30	-	$4.97		920,023	$	4.52		8.11		409,403	$	4.55
$5.01	-	$5.67		510,696	$	5.37		7.11		317,831	$	5.37
$6.00	-	$6.61		242,627	$	6.03		6.29		209,608	$	6.01
$7.00	-	$7.92		238,024	$	7.70		7.04		162,900	$	7.71
$9.92	-	$9.92		10,424	$	9.92		3.60		10,424	$	9.92
$59.60	-	$149.04		10	$	149.04		2.31		10	$	149.04
Total:				5,314,375	$	3.00		8.64		1,790,963	$	4.26

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Expected term (in years)		5			5			5			5
Average volatility		75	%		69	%		73	%		75	%
Risk-free interest rate		2.03	%		2.82	%		2.49	%		2.63	%
Dividend yield		0	%		0	%		0	%		0	%

	Three Months Ended					Six Months Ended
	June 30,					June 30,
	2019		2018			2019			2018
Expected term (in years)		N/A		10			5			10
Average volatility		N/A		91	%		73	%		91	%
Risk-free interest rate		N/A		2.85	%		2.49	%		2.85	%
Dividend yield		N/A		0	%		0	%		0	%

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Cost of revenue	$	34	$	17	$	66	$	28
Research and development		53		65		93		187
Selling, general and administrative		534		693		958		1,314
Total	$	621	$	775	$	1,117	$	1,529

2017 Employee Stock Purchase Plan [Member]

Notes Tables

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Expected term (in years)		0.25			0.25			0.25			0.25
Average volatility		87	%		74	%		81	%		67	%
Risk-free interest rate		2.43	%		1.73	%		2.44	%		1.58	%
Dividend yield		0	%		0	%		0	%		0	%