Net Loss Per Shares (Details 2) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
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	29,113	31,387
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	25,350	26,665
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	2,492	3,981
Non-vested restricted stock 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	1,271	741