Stockholders' Equity (Details 2) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Number of Shares
Balance at the end of the period (in shares)	4,657,949
Stock options
Number of Shares
Balance at the beginning of the period (in shares)	3,574,450
Granted (in shares)	1,554,960
Exercised (in shares)	(317,681)
Forfeitures (in shares)	(153,780)
Balance at the end of the period (in shares)	4,657,949	3,574,450
Vested or expected to vest at the end of the period (in shares)	4,500,954
Exercisable at the end of the period (in shares)	1,830,274
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 3.75
Granted (in dollars per share)	6.95
Exercised (in dollars per share)	2.15
Forfeitures/Expirations (in dollars per share)	6.04
Balance at the end of the period (in dollars per share)	4.85	$ 3.75
Vested or expected to vest at the end of the period (in dollars per share)	4.78
Exercisable at the end of the period (in dollars per share)	$ 2.96
Weighted Average Remaining Contractual Term
Options Outstanding at the end of the period	8 years 29 days	8 years 22 days