Common and Preferred Stock - Common Stock Reserved for Issuance (Details) - shares
Dec. 31, 2015
Mar. 11, 2015
Feb. 10, 2015
Jan. 31, 2015
Dec. 31, 2014
Common Stock Reserved for Issuance          
Total shares reserved 6,261,008       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 1,521,843       0
2015 Employee Stock Purchase Plan          
Common Stock Reserved for Issuance          
Total shares reserved 241,272     375,000 0
Stock Options          
Common Stock Reserved for Issuance          
Total shares reserved 4,297,893       3,425,117
Lender Warrants and Additional Lender Warrant to purchase common stock          
Common Stock Reserved for Issuance          
Total shares reserved 200,000       150,000
Series A convertible preferred stock          
Common Stock Reserved for Issuance          
Total shares reserved 0       2,383,745
Series B convertible preferred stock          
Common Stock Reserved for Issuance          
Total shares reserved 0       3,649,368
Series C convertible preferred stock          
Common Stock Reserved for Issuance          
Total shares reserved 0       5,406,501
Series D convertible preferred stock          
Common Stock Reserved for Issuance          
Total shares reserved 0       3,409,210