Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Total revenues	$ 1,194,000	$ 20,759,000	$ 7,669,000
Operating expenses:
Research and development	64,305,000	56,387,000	41,046,000
General and administrative	18,391,000	19,130,000	11,533,000
Total operating expenses	82,696,000	75,517,000	52,579,000
Loss from operations	(81,502,000)	(54,758,000)	(44,910,000)
Other income (expense):
Interest and other income	844,000	855,000	388,000
Interest and other expense	(1,182,000)	(52,000)	(39,000)
Loss from valuation of convertible note payable	0	(1,811,000)	(12,118,000)
Loss before income taxes	(81,840,000)	(55,766,000)	(56,679,000)
Income tax benefit (expense)	4,000	18,000	(1,000)
Net loss	(81,836,000)	(55,748,000)	(56,680,000)
Other comprehensive loss:
Unrealized gain (loss) on short-term investments, net	10,000	64,000	(181,000)
Comprehensive loss	$ (81,826,000)	$ (55,684,000)	$ (56,861,000)
Net loss per share - basic and diluted (in dollars per share)	$ (1.55)	$ (1.08)	$ (1.29)
Weighted average shares used to compute basic and diluted net loss per share (in shares)	52,813,474	51,411,353	44,090,165
Strategic Alliances and Collaborations
Revenues:
Total revenues	$ 1,194,000	$ 20,759,000	$ 7,669,000