Prepaid expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Director compensation	$ 215	$ 6
Director and officer insurance	70
Legal retainer	25
Rent	17	16
Engineering, software licenses and other	10	14
Total prepaid expenses	$ 337	$ 36