Redeemable Convertible Preferred Stock - Schedule of Redeemable Convertible Preferred Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Series A Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock , Years Issued	2002 – 2004
Redeemable convertible preferred stock , Shares Issued	1,292,084
Redeemable convertible preferred stock , Net Proceeds	$ 1,307,794
Series B Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock , Years Issued	2005 – 2006
Redeemable convertible preferred stock , Shares Issued	11,919,624
Redeemable convertible preferred stock , Net Proceeds	3,542,237
Series C-1 Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock , Years Issued	2007
Redeemable convertible preferred stock , Shares Issued	16,240,450
Redeemable convertible preferred stock , Net Proceeds	5,505,641
Series C-2 Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock , Years Issued	2008 – 2009
Redeemable convertible preferred stock , Shares Issued	19,104,610
Redeemable convertible preferred stock , Net Proceeds	4,172,672
Series D Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock , Years Issued	2011 – 2015
Redeemable convertible preferred stock , Shares Issued	143,762,592
Redeemable convertible preferred stock , Net Proceeds	30,947,799
Series E Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock , Years Issued	2014 – 2015
Redeemable convertible preferred stock , Shares Issued	45,989,722
Redeemable convertible preferred stock , Net Proceeds	$ 7,395,228