CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - TEMPORARY EQUITY - USD ($) shares in Thousands, $ in Thousands	Convertible Preferred Stock Series C convertible preferred stock	Convertible Preferred Stock Series D convertible preferred stock	Convertible Preferred Stock Series F convertible preferred stock	Convertible Preferred Stock	Series C convertible preferred stock	Series D convertible preferred stock	Series F convertible preferred stock	Total
Balance at Dec. 31, 2012				$ 126,210
Balance (in shares) at Dec. 31, 2012				18,118
Convertible Preferred Stock
Issuance of convertible preferred stock			$ 19,227
Issuance of convertible preferred stock (in shares)			2,173
Conversion of convertible notes payable and accrued interest into Series F convertible preferred stock at $8.85 per share			$ 10,773
Conversion of convertible notes payable and accrued interest into Series F convertible preferred stock at $8.85 per share (in shares)			1,217
Balance at Dec. 31, 2013				$ 156,210
Balance (in shares) at Dec. 31, 2013				21,508
Convertible Preferred Stock
Issuance of convertible preferred stock in connection with exercises of preferred stock warrants	$ 836	$ 333
Issuance of convertible preferred stock in connection with exercises of preferred stock warrants (in shares)	105	29
Balance at Dec. 31, 2014				$ 157,379	$ 40,836	$ 41,496	$ 30,000	$ 157,379
Balance (in shares) at Dec. 31, 2014				21,642	5,819	5,410	3,390