Net Loss per Share - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	7,651,141	6,986,783
Employee stock options
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	4,577,587	3,772,561
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)	279,997	423,572
ESPP rights
Potentially dilutive securities have been excluded from diluted net loss per share calculations
Anti-dilutive securities (in shares)	43,557	40,650