Summary of Significant Accounting Policies - Net Loss per Share (Details) - shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders	62,088,366	49,317,111
Convertible Preferred Stock
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders	59,958,081	47,243,931
Stock options
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders	2,029,402	1,600,303
Restricted stock
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders	100,883	472,877