Net Loss Per Share (Details 2) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Convertible preferred stock
Net Loss Per Share
Potentially dilutive securities, prior to the use of the treasury stock method, excluded from the computation of diluted weighted-average shares outstanding, as they would be anti-dilutive		3,857,664	6,617,686
Options to purchase common stock
Net Loss Per Share
Potentially dilutive securities, prior to the use of the treasury stock method, excluded from the computation of diluted weighted-average shares outstanding, as they would be anti-dilutive	3,903,051	2,466,492	1,743,890
Warrants
Net Loss Per Share
Potentially dilutive securities, prior to the use of the treasury stock method, excluded from the computation of diluted weighted-average shares outstanding, as they would be anti-dilutive	822,726	1,271,520	545,797