Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ 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	$ 27,453	$ 18,217	$ 81,827	$ 46,054
General and administrative	19,240	8,456	50,079	19,212
Loss from operations	(46,693)	(26,673)	(131,906)	(65,266)
OTHER (EXPENSE) INCOME:
Other (expense) income, net	(78)	1	(174)	(127)
Loss on retirement of note payable	0	(1,572)	0	(1,572)
Interest income	585	274	1,996	564
Interest expense	0	(294)	0	(1,885)
NET LOSS	(46,186)	(28,264)	(130,084)	(68,286)
OTHER COMPREHENSIVE LOSS, NET OF TAX:
Unrealized (loss) gain from available-for-sale securities	(136)	89	47	120
COMPREHENSIVE LOSS	(46,322)	(28,175)	(130,037)	(68,166)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED	$ (46,186)	$ (28,264)	$ (130,084)	$ (68,286)
LOSS PER SHARE:
Basic and diluted (in dollars per share)	$ (1.07)	$ (0.68)	$ (3.02)	$ (1.77)
WEIGHTED AVERAGE SHARES:
Basic and diluted (in shares)	43,092,921	41,331,612	43,049,734	38,525,827