Stock-Based Compensation - Summary of Stock Options Activity (Details) - Employee Stock Option - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Options
Beginning balance (in shares)	6,948,630	4,913,472	4,287,545
Granted (in shares)	3,246,250	2,688,500	1,410,038
Exercise (in shares)	(1,335,271)	(265,166)
Forfeitures (in shares)	(3,330,981)	(388,176)	(784,111)
Ending balance (in shares)	5,528,628	6,948,630	4,913,472	4,287,545
Vested and exercisable (in shares)	2,415,461
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding (in USD per share)	$ 5.45	$ 4.66	$ 5.18
Granted (in USD per share)	5.02	7.02	4.42
Exercised (in USD per share)	3.81	3.25
Forfeited (in USD per share)	5.63	7.75	7.08
Outstanding (in USD per share)	5.49	$ 5.45	$ 4.66	$ 5.18
Vested and exercisable (in USD per share)	$ 5.18
Intrinsic value, outstanding	$ 0	$ 5,903,466	$ 2,808,083	$ 5,896,329
Intrinsic value, vested and exercisable	$ 0
Weighted average remaining contract term, outstanding	7 years 7 months 28 days	7 years 9 months 11 days	7 years 7 months 6 days	6 years 8 months 12 days
Weighted average remaining contractual term, exercisable	6 years 4 months 17 days