STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Collaboration revenue	$ 1,697	$ 272	$ 3,666	$ 544
Operating expenses:
Research and development, including costs of contracts	129,228	7,424	139,427	81,673
General and administrative	3,711	7,073	7,521	11,323
Total operating expenses	132,939	14,497	146,948	92,996
Loss from operations	(131,242)	(14,225)	(143,282)	(92,452)
Other income (expense), net	42	14	63	10
Net loss	$ (131,200)	$ (14,211)	$ (143,219)	$ (92,442)
Net loss per share - basic and diluted	$ (1.01)	$ (0.11)	$ (1.10)	$ (0.76)
Weighted average common shares outstanding used to compute net loss per share - basic and diluted	130,385,077	128,413,417	130,271,806	120,953,279