Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating expenses:
Research and development	$ 34,349	$ 36,673	$ 117,523	$ 105,018
General and administrative	22,184	15,090	60,812	50,714
Total operating expenses	56,533	51,763	178,335	155,732
Operating loss	(56,533)	(51,763)	(178,335)	(155,732)
Other income (loss):
Interest (expense) income and other, net	(209)	(176)	(478)	383
Total other (loss) income	(209)	(176)	(478)	383
Net loss	(56,742)	(51,939)	(178,813)	(155,349)
Other comprehensive income (loss):
Unrealized (loss) gain on short-term securities - available-for-sale	(1)	18	111	94
Total other comprehensive (loss) income	(1)	18	111	94
Comprehensive loss	$ (56,743)	$ (51,921)	$ (178,702)	$ (155,255)
Net loss per share — basic and diluted	$ (1.18)	$ (1.25)	$ (3.83)	$ (3.75)
Weighted average number of shares of common stock outstanding for computing basic and diluted net loss per share	48,254	41,565	46,709	41,416