Stockholders' Equity - Options Outstanding (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Number of Shares
Balance at the beginning of the period (in shares)	6,370,578
Granted (in shares)	2,826,844
Exercised (in shares)	(283,995)
Forfeited/Cancelled (in shares)	(393,275)
Balance at the end of the period (in shares)	8,520,152	6,370,578
Vested or expected to vest at the end of the period (in shares)	8,520,152
Exercisable at the end of the period (in shares)	3,514,623
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 6.10
Granted (in dollars per share)	4.72
Exercised (in dollars per share)	1.25
Forfeitures/Expirations (in dollars per share)	6.80
Balance at the end of the period (in dollars per share)	5.78	$ 6.10
Vested or expected to vest at the end of the period (in dollars per share)	5.78
Exercisable at the end of the period (in dollars per share)	$ 5.19
Weighted Average Remaining Contractual Term
Options Outstanding at the end of the period	8 years 7 days	7 years 7 months 6 days
Vested or expected to vest at the end of the period	8 years 7 days
Exercisable at the end of the period	6 years 6 months 29 days