Quarterly financial information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Details
Revenue	$ 1,217	$ 964	$ 1,870	$ 1,801	$ 2,727	$ 2,613	$ 1,295	$ 1,730	$ 5,852	$ 8,365
Gross margin (loss)	1,164	880	1,007	1,000	1,238	1,475	1,328	(2,600)	4,051	1,441
Net loss	$ (2,421)	$ (3,667)	$ (3,436)	$ (3,654)	$ (4,074)	$ (3,845)	$ (4,971)	$ (9,803)	$ (13,178)	$ (22,693)
Net loss per share - basic and diluted	$ (0.08)	$ (0.13)	$ (0.13)	$ (0.14)	$ (0.16)	$ (0.15)	$ (0.26)	$ (0.58)	$ (0.47)	$ (1.05)