Stockholder's Equity - Shares Reserved for Future Grant and Issuance (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Shares Reserved for Future Issuance
Stock options outstanding (in shares)		7,590,430	7,568,304
Warrants outstanding (in shares)		623,091
Total shares of common stock reserved for issuance (in shares)		19,730,637
2013 plan
Shares Available for Future Grant
Balance at the beginning of the period (in shares)	4,394,301
Authorized (in shares)	3,768,550
Granted (in shares)	(480,000)
Forfeitures/Expirations (in shares)	302,524
Balance at the end of the period (in shares)	7,985,375
Shares Reserved for Future Issuance
Shares available for future grant (in shares)	7,985,375	7,985,375	4,394,301
Inducement Plan
Shares Available for Future Grant
Balance at the beginning of the period (in shares)	205,000
Forfeitures/Expirations (in shares)	23,750
Balance at the end of the period (in shares)	228,750
Shares Reserved for Future Issuance
Shares available for future grant (in shares)	228,750	228,750	205,000
Employee Stock Purchase Plan [Member]
Shares Reserved for Future Issuance
Total shares of common stock reserved for issuance (in shares)		225,806
Employee Stock Option | 2013 plan
Shares Reserved for Future Issuance
Stock options outstanding (in shares)		7,319,180
Employee Stock Option | Inducement Plan
Shares Reserved for Future Issuance
Stock options outstanding (in shares)		271,250
Restricted Stock Units | 2013 plan
Shares Reserved for Future Issuance
Total shares of common stock reserved for issuance (in shares)		3,077,185