Summary of Significant Accounting Policies - Schedule of Anti-dilutive Common Stock Equivalents Excluded from the Calculation of Diluted Net Income (Loss) per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Income (Loss) Per Share
Anti-dilutive common stock equivalents excluded from the calculation of diluted net income (loss) per share (in shares)	4,279	4,178	4,135
Stock Options
Net Income (Loss) Per Share
Anti-dilutive common stock equivalents excluded from the calculation of diluted net income (loss) per share (in shares)	3,820	3,513	3,452
Common Stock Warrants
Net Income (Loss) Per Share
Anti-dilutive common stock equivalents excluded from the calculation of diluted net income (loss) per share (in shares)	39	39	61
Shares issuable under employee stock purchase plan
Net Income (Loss) Per Share
Anti-dilutive common stock equivalents excluded from the calculation of diluted net income (loss) per share (in shares)	23	18	18
Restricted Stock Units
Net Income (Loss) Per Share
Anti-dilutive common stock equivalents excluded from the calculation of diluted net income (loss) per share (in shares)	397	608	604