Net Income (Loss) Per Share - Anti-dilutive shares excluded from the calculation of diluted net loss per share (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Anti-dilutive shares excluded from the calculation of diluted net loss per share attributable to common stockholders
Total shares excluded from net loss per share	13,912	18,728
Options to purchase common stock
Anti-dilutive shares excluded from the calculation of diluted net loss per share attributable to common stockholders
Total shares excluded from net loss per share	9,219	10,884
Common stock warrants
Anti-dilutive shares excluded from the calculation of diluted net loss per share attributable to common stockholders
Total shares excluded from net loss per share	1,459	1,459
Non-vested restricted stock unit awards
Anti-dilutive shares excluded from the calculation of diluted net loss per share attributable to common stockholders
Total shares excluded from net loss per share	3,234	6,385