CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
Government contracts	$ 33,344	$ 26,213	$ 17,708
Research and development collaborations	2,906	4,446	3,207
Total revenue	36,250	30,659	20,915
Expenses:
Research and development	162,644	94,422	58,530
General and administrative	30,842	19,928	14,819
Total expenses	193,486	114,350	73,349
Loss from operations	(157,236)	(83,691)	(52,434)
Other income (expense):
Investment income	660	286	187
Interest expense	(241)	(157)	(160)
Other income (expense), net	(120)	0	182
Realized gains on marketable securities	0	615	0
Change in fair value of warrant liability	0	0	267
Loss from operations before income tax expense	(156,937)	(82,947)	(51,958)
Income tax expense	0	0	25
Net loss	$ (156,937)	$ (82,947)	$ (51,983)
Basic and diluted net loss per share (in dollars per share)	$ (0.6)	$ (0.37)	$ (0.31)
Basic and diluted weighted average number of common shares outstanding (in shares)	262,248	225,848	169,658