Net Loss Per Shares (Details 2) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
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	18,728	21,454
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	10,884	14,564
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	6,385	5,431