Condensed Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		64 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Operating expenses
Research and development	$ 4,869	$ 3,499	$ 50,742
General and administrative	2,714	682	12,855
Total operating expenses	7,583	4,181	63,597
Loss from operations	(7,583)	(4,181)	(63,597)
Interest income			3
Interest expense		(128)	(863)
Other income (expense), net	(11,843)	290	(9,813)
Net loss and comprehensive loss	(19,426)	(4,019)	(74,270)
Deemed dividend related to beneficial conversion feature of convertible preferred stock	(25,559)		(25,559)
Accretion of Series A preferred stock to redemption value, net of extinguishment			1,098
Net loss attributable to common stockholders	$ (44,985)	$ (4,019)	$ (98,731)
Net loss per basic and diluted share attributable to common stockholders	$ (16.13)	$ (30.23)
Weighted-average common shares used to compute basic and diluted net loss per share	2,788,087	132,969