Note 3 - Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2018

Notes Tables

Property, Plant and Equipment, Weighted Average Useful Life [Table Text Block]

Machinery and equipment	5 years
Computer equipment	3 years
Furniture and fixtures	5 years
Software licenses	1 - 3 years
Office equipment	3 years

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

	March 31, 2018
	Fair Value Measurements
	Using Input Types
	Level 1		Level 2		Level 3		Total
Cash and cash equivalents	$	1,182	$	—	$	—	$	1,182
Short-term investments		12,441		—		—		12,441
Total assets at fair value	$	13,623	$	—	$	—	$	13,623

	Dec 31, 2017
	Fair Value Measurements
	Using Input Types
	Level 1		Level 2		Level 3		Total
Cash and cash equivalents	$	4,162	$	—	$	—	$	4,162
Short-term investments		18,428		—		—		18,428
Total assets at fair value	$	22,590	$	—	$	—	$	22,590

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	2018		2017
Shares of common stock issuable upon exercise of warrants		615		337
Shares of common stock issuable upon exercise of stock options		8,153		5,695
Potential common shares excluded from diluted net loss per share		8,768		6,032