Net Loss Per Share (Details 2) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 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 (in shares)	0	0	3,857,664
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 (in shares)	5,815,168	3,903,051	2,466,492
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 (in shares)	630,444	822,726	1,271,520
Restricted Stock Units (RSUs)
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 (in shares)	42,363	0	0