Net Loss per Share - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	6,750,278	6,399,025	2,463,089
Employee stock options
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	3,681,521	3,178,441	2,438,151
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)	278,482	418,450
ESPP rights
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	40,275	52,134	24,938