Stock Option Plan - Summary of stock-based compensation activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Stock Options Outstanding
Balance	1,909,911	649,500
Granted	160,000	1,308,017
Exercised		(7,051)
Forfeited/Cancelled	(20,394)	(40,555)
Balance	2,049,517	1,909,911
Exercisable	1,643,417	1,464,189
Weighted Average Exercise Price
Balance	$ 2.58	$ 1.49
Granted	2.23	3.15
Exercised		2.10
Forfeited/Cancelled	2.23	2.29
Balance	2.58	2.58
Exercisable	$ 2.60	$ 2.60
Weighted Average Remaining Contractual Term, Options Outstanding (in years)	7 years 7 months 28 days	8 years 6 months 22 days	7 years 5 months 9 days
Weighted Average Remaining Contractual Term, Options Exercisable (in years)	7 years 7 months 28 days	8 years 3 months 26 days
Aggregate Intrinsic Value, Options exercised		$ 17
Aggregate Intrinsic Value, Options Outstanding	$ 306	813	$ 474
Aggregate Intrinsic Value, Options Exercisable	$ 306	$ 713