STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaboration Revenue	$ 4,332	$ 1,373	$ 800
Operating expenses:
Research and development	106,785	32,706	42,852
General and administrative	17,647	12,166	15,661
Total operating expenses	124,432	44,872	58,513
Loss from operations	(120,100)	(43,499)	(57,713)
Other income (expense), net	12	(5)	(579)
Change in fair value of warrants		11,723	1,185
Net loss	$ (120,088)	$ (31,781)	$ (57,107)
Basic and diluted net loss per share	$ (0.96)	$ (0.31)	$ (0.66)
Weighted average common shares outstanding used to compute basic and diluted net loss per share	125,416,084	101,130,710	85,943,175