Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options outstanding (in shares), beginning	4,299,810	4,105,369	3,592,734
Number of options granted (in shares)	839,785	577,845	739,135
Number of options exercised (in shares)	(239,000)	(171,566)	(61,834)
Number of options expired (in shares)	0	0	0
Number of options forfeited (in shares)	(548,204)	(211,838)	(164,666)
Number of options outstanding (in shares), ending	4,352,391	4,299,810	4,105,369
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Shares issuable under options exercise price per share (in dollars per share)	$ 5.09	$ 4.76	$ 4.36
Granted, exercise price per share (in dollars per share)	3.34	7.15	7.26
Exercised, exercise price per share (in dollars per share)	1.05	1.92	1.54
Expired, exercise price per share (in dollars per share)	0	0	0
Forfeited, exercise price per share (in dollars per share)	8.04	7.70	8.37
Shares issuable under options exercise price per share (in dollars per share)	4.61	5.09	4.76
Minimum
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Shares issuable under options exercise price per share (in dollars per share)	0.79	0.79	0.79
Granted, exercise price per share (in dollars per share)	1.73	3.38	4.72
Exercised, exercise price per share (in dollars per share)	1.02	0.79	1.10
Forfeited, exercise price per share (in dollars per share)	2.02	4.80	4.55
Shares issuable under options exercise price per share (in dollars per share)	0.79	0.79	0.79
Maximum
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Shares issuable under options exercise price per share (in dollars per share)	10.67	10.67	10.67
Granted, exercise price per share (in dollars per share)	4.25	9.28	8.81
Exercised, exercise price per share (in dollars per share)	1.83	5.85	6.51
Forfeited, exercise price per share (in dollars per share)	10.67	10.67	10.67
Shares issuable under options exercise price per share (in dollars per share)	$ 10.67	$ 10.67	$ 10.67