Stock-based Compensation - Service-based stock options (Details) - Service Based Stock Options - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Service-based stock options activity
Shares outstanding, beginning (in shares)	1,894,083
Granted (in shares)	524,147
Exercised (in shares)	0
Expired (in shares)	(2,887)
Forfeited (in shares)	(3,955)
Shares outstanding, ending (in shares)	2,411,388	1,894,083
Exercisable at September 30, 2017 (in shares)	1,193,791
Vested and expected to vest at September 30, 2017 (in shares)	2,411,388
Service-based stock options weighted average exercise price
Beginning balance, Weighted average exercise price (in dollars per share)	$ 3.09
Granted, Weighted average exercise price (in dollars per share)	5.90
Exercised, Weighted average exercise price (in dollars per share)	0.00
Expired, Weighted average exercise price (in dollars per share)	5.68
Forfeited, Weighted average exercise price (in dollars per share)	3.05
Ending balance, Weighted average exercise price (in dollars per share)	3.70	$ 3.09
Options exercisable, Weighted average exercise price per share (in dollars per share)	1.99
Vested and expected to vest, Weighted average exercise price per share (in dollars per share)	$ 3.70
Service-based stock options, additional disclosures
Options outstanding, Weighted average remaining contractual life	6 years 8 months 1 day	6 years 8 months 2 days
Options exercisable, Weighted average remaining contractual life	4 years 1 month 2 days
Vested and expected to vest, Weighted average remaining contractual life	6 years 8 months 1 day