Stockholders' Equity - Shares Available for Future Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity
Employee stock purchase plan (in shares)	225,806
Warrants outstanding (in shares)	623,091
Total shares of common stock reserved for future issuance (in shares)	15,962,087
2013 plan
Stockholders' Equity
Stock options outstanding (in shares)	7,273,304
Shares available for future grant (in shares)	4,394,301	2,603,983
2013 plan | Restricted Stock Units
Stockholders' Equity
Stock options outstanding (in shares)	2,945,585
Inducement Plan
Stockholders' Equity
Stock options outstanding (in shares)	295,000
Shares available for future grant (in shares)	205,000	144,125