Stock Option Plan - Summary of stock-based compensation activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Number of Stock Options Outstanding
Balance, January 1, 2016	1,909,911
Options granted	160,000
Options exercised
Options forfeited/canceled	394
Balance, June 30, 2016	2,069,517	1,909,911
Exercisable as of June 30, 2016	1,581,140
Weighted Average Exercise Price
Balance, January 1, 2016	$ 2.58
Options granted	2.23
Options exercised
Options forfeited/canceled	3.44
Balance, June 30, 2016	2.58	$ 2.58
Exercisable as of June 30, 2016	$ 2.61
Weighted Average Remaining Contractual Term, Options Outstanding (in years)	8 years 2 months 5 days	8 years 6 months 22 days
Weighted Average Remaining Contractual Term, Options Exercisable (in years)	7 years 11 months 1 day
Aggregate Intrinsic Value, Options Outstanding	$ 280	$ 813
Aggregate Intrinsic Value, Options Exercisable	$ 280