Net Loss Per Shares (Details 2) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
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	27,297	30,011
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	21,823	23,966
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	1,605
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	4,015	4,440