Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 300	$ 383	$ 617
Operating expenses:
Research and development	47,529	33,390	27,831
General and administrative	25,088	19,043	11,011
Total operating expenses	72,617	52,433	38,842
Loss from operations	(72,317)	(52,050)	(38,225)
Interest income	231	44	2
Interest expense	(1,190)	(10,672)	(15,164)
Change in fair value of derivative liabilities associated with the convertible notes	0	4,032	2,660
Changes in fair value of derivative liabilities associated with Medicis settlement	127	(320)	47
Change in fair value of common stock warrant liability	0	(2,151)	(621)
Change in fair value of convertible preferred stock warrant liability	0	(210)	(743)
Loss on settlement of preferred stock warrant	0	(1,356)	0
Other expense, net	(327)	(234)	(404)
Net loss	(73,476)	(62,917)	(52,448)
Unrealized loss on available for sale securities	(40)	0	0
Comprehensive loss	(73,516)	(62,917)	(52,448)
Net income (loss) attributable to common stockholders (Note 15):
Basic	(73,476)	(62,917)	258
Diluted	$ (73,476)	$ (62,917)	$ 1,083
Net income (loss) per share attributable to common stockholders:
Basic (in dollars per share)	$ (3.02)	$ (3.24)	$ 1.17
Diluted (in dollars per share)	$ (3.02)	$ (3.24)	$ 1.05
Weighted-average number of shares used in computing net income (loss) per share attributable to common stockholders:
Basic (in shares)	24,340,466	19,391,523	220,220
Diluted (in shares)	24,340,466	19,391,523	1,029,150