Net Loss Per Share (Details 2) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
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		7,043,931		7,779,266
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	3,747,303	2,621,820	3,562,712	2,373,083
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	846,720	1,311,356	979,434	1,161,639