Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating expenses:
Research and development	$ 44,348	$ 29,180	$ 83,174	$ 68,345
General and administrative	17,752	12,927	38,628	35,624
Total operating expenses	62,100	42,107	121,802	103,969
Operating loss	(62,100)	(42,107)	(121,802)	(103,969)
Other income (loss):
Interest (expense) income and other, net	(201)	256	(269)	559
Total other (loss) income	(201)	256	(269)	559
Net loss	(62,301)	(41,851)	(122,071)	(103,410)
Other comprehensive income (loss):
Unrealized gain (loss) on short-term securities - available-for-sale	6	(2)	112	76
Total other comprehensive income (loss)	6	(2)	112	76
Comprehensive loss	$ (62,295)	$ (41,853)	$ (121,959)	$ (103,334)
Net loss per share — basic and diluted	$ (1.35)	$ (1.01)	$ (2.66)	$ (2.50)
Weighted average number of shares of common stock outstanding for computing basic and diluted net loss per share	46,157	41,357	45,927	41,341