Note 13 - Quarterly Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Revenues	$ 21	$ 227	$ 38	$ 18	$ 16	$ 305	$ 11	$ 4
Gross profit (loss)	(22)	(64)	38	18	(59)	23	11	4
Operating loss	(3,889)	(3,651)	(3,751)	(2,718)	(2,883)	(2,375)	(2,453)	(2,648)
Net loss	$ (7,216)	$ (5,965)	$ (5,990)	$ (4,842)	$ (5,106)	$ (4,566)	$ (4,515)	$ (4,648)
Basic and diluted net loss per common share (in dollars per share)	$ (0.40)	$ (0.33)	$ (0.34)	$ (0.27)	$ (0.30)	$ (0.28)	$ (0.28)	$ (0.29)