Note 8 - Stock-based Compensation (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2019

Dec. 31, 2018

Notes Tables

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of revenues	$	40	$	20	$	128	$	56
Research and development expenses		122		137		339		353
Selling, general and administrative expenses		361		611		1,065		1,619
	$	523	$	768	$	1,532	$	2,028

	Year Ended December 31,
	2018		2017
Cost of revenues	$	97	$	269
Research and development expenses		547		1,766
Selling, general and administrative expenses		2,436		2,931
	$	3,080	$	4,966