Common and Preferred Stock - Common Stock Reserved for Future Issuance (Details) - shares
Jun. 30, 2015
Mar. 11, 2015
Feb. 10, 2015
Jan. 31, 2015
Dec. 31, 2014
Common Stock Reserved for Issuance          
Total shares reserved 6,570,241       18,423,941
Common shares authorized 500,000,000 500,000,000 25,000,000   22,000,000
Equity Incentive Plans          
Common Stock Reserved for Issuance          
Total shares reserved 2,610,701        
2015 Employee Stock Purchase Plan          
Common Stock Reserved for Issuance          
Total shares reserved 375,000     375,000  
Stock Options          
Common Stock Reserved for Issuance          
Total shares reserved 3,384,540       3,425,117
Lender and Additional Lender Warrants to Purchase Common Stock          
Common Stock Reserved for Issuance          
Total shares reserved 200,000       150,000
Convertible Series A Preferred Stock          
Common Stock Reserved for Issuance          
Total shares reserved         2,383,745
Convertible Series B Preferred Stock          
Common Stock Reserved for Issuance          
Total shares reserved         3,649,368
Convertible Series C Preferred Stock          
Common Stock Reserved for Issuance          
Total shares reserved         5,406,501
Convertible Series D Preferred Stock          
Common Stock Reserved for Issuance          
Total shares reserved         3,409,210