Stock Option Plan - Summary of stock-based compensation activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Number of Stock Options Outstanding
Balance, January 1, 2017	2,049,517
Options granted	175,000
Options exercised	(150,000)
Forfeited/Cancelled	(155,417)
Balance, June 30, 2017	1,919,100
Exercisable as of June 30, 2017	1,424,741
Weighted Average Exercise Price
Balance, January 1, 2017	$ 2.58
Options granted	2
Options exercised	0.52
Options forfeited/canceled	3.46
Balance, June 30, 2017	2.62
Exercisable as of June 30, 2017	$ 2.72
Weighted Average Remaining Contractual Term, Options Outstanding (in years)	7 years 10 months 10 days	7 years 7 months 28 days
Weighted Average Remaining Contractual Term, Options Exercisable (in years)	7 years 7 months 6 days
Aggregate Intrinsic Value, Options Outstanding	$ 626	$ 306
Aggregate Intrinsic Value, Options Exercisable	$ 453