Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended	37 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2013
Stock, par value per share	$ 0.0001			$ 0.0001
Common Stock [Member] | IPO [Member]
Convertible preferred stock, issuance cost	$ 2,620
Series A Preferred Stock [Member] | Issuance Date of December 2008 [Member]
Stock, par value per share		$ 0.0001
Series A Preferred Stock [Member] | Issuance Date of May and December 2009 and April 2010 [Member]
Stock, issuance price per share		$ 1.00
Convertible preferred stock, issuance cost		3
Series B Preferred Stock [Member] | Issuance Date of February 2011 [Member]
Stock, issuance price per share		$ 0.45
Convertible preferred stock, issuance cost		210
Series B Preferred Stock [Member] | Issuance Date of February 2011 [Member] | Convertible notes [Member]
Stock, issuance price per share		$ 0.45
Series B Preferred Stock [Member] | Issuance Date of January 2012 [Member]
Stock, issuance price per share			$ 0.45
Convertible preferred stock, issuance cost			23
Convertible preferred stock, call option liability			129
Series B Preferred Stock [Member] | Issuance Date of May 2012 [Member]
Stock, issuance price per share			$ 0.45
Convertible preferred stock, call option liability			132
Series C Convertible Preferred Stock [Member]
Stock, issuance price per share				$ 0.56
Convertible preferred stock, issuance cost				335
Convertible preferred stock, call option liability				864
Series D Preferred Stock [Member]
Stock, issuance price per share				$ 0.56
Convertible preferred stock, issuance cost				209
Convertible preferred stock, call option liability				126
Series D-2 Preferred [Member] | Issuance Date of January and May 2012 [Member]
Stock, issuance price per share	$ 0.76
Convertible preferred stock, issuance cost	23
Series E Preferred Stock [Member] | Issuance Date of January and May 2012 [Member]
Stock, issuance price per share	$ 1.13
Convertible preferred stock, issuance cost	$ 184