Net Loss Per Share - Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	4,902	5,447	6,093
Stock options outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	2,530	3,122	4,047
Restricted stock units outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	2,372	2,325	2,033
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share
Anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	0	0	13