Net Loss per Share - Antidilutive Securities (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	7,588,812	6,936,015
Employee stock options
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	4,537,986	3,780,445
Common stock warrants
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	2,750,000	2,750,000
Restricted stock units
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	262,608	368,571
ESPP rights
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	38,218	36,999