Net Loss Per Share Attributable to Common Stockholders - Potential Dilutive Securities Excluded from Computation of Diluted Net Loss Per Common Share (Detail)
6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Options to Purchase Common Stock [Member]
   
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potential dilutive securities excluded from computation of diluted net loss per common share 2,524,396 2,375,882
Warrants to Purchase Common Stock [Member]
   
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potential dilutive securities excluded from computation of diluted net loss per common share 74,412  
Warrants to Purchase Redeemable Convertible Preferred Stock [Member]
   
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potential dilutive securities excluded from computation of diluted net loss per common share   74,412
Redeemable Convertible Preferred Stock [Member]
   
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potential dilutive securities excluded from computation of diluted net loss per common share   8,738,085
Unvested Restricted Stock [Member]
   
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Potential dilutive securities excluded from computation of diluted net loss per common share   107,696