Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues:
Total revenues	$ 20,759	$ 7,669	$ 19,569
Operating expenses:
Research and development	56,387	41,046	29,942
General and administrative	19,130	11,533	7,429
Total operating expenses	75,517	52,579	37,371
Loss from operations	(54,758)	(44,910)	(17,802)
Other income (expense):
Interest and other income	855	388	292
Interest and other expense	(52)	(39)	(36)
Loss from valuation of convertible note payable	(1,811)	(12,118)	(1,145)
Loss before income taxes	(55,766)	(56,679)	(18,691)
Income tax benefit (expense)	18	(1)	23
Net loss	(55,748)	(56,680)	(18,668)
Other comprehensive loss:
Unrealized gain (loss) on short-term investments, net	64	(181)	36
Comprehensive loss	$ (55,684)	$ (56,861)	$ (18,632)
Net loss per share - basic and diluted (in dollars per share)	$ (1.08)	$ (1.29)	$ (0.49)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	51,411,353	44,090,165	38,479,447
Strategic Alliances and Collaborations
Revenues:
Total revenues	$ 20,759	$ 7,669	$ 19,569