Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING EXPENSES:
Research and development	$ 68,280	$ 45,719	$ 60,536
General and administrative	30,797	13,674	6,829
Loss from operations	(99,077)	(59,393)	(67,365)
OTHER INCOME (EXPENSE) :
Other (expense) income, net	(35)	(510)	9,085
Loss on retirement of note payable	(1,572)	(203)
Interest income	1,043	94	30
Interest expense	(1,885)	(2,467)	(2,440)
NET LOSS	(101,526)	(62,479)	(60,690)
OTHER COMPREHENSIVE INCOME, NET OF TAX:
Unrealized gain (loss) from marketable securities	26	(21)
COMPREHENSIVE LOSS	(101,500)	(62,500)	(60,690)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED (Note 12)	$ (101,526)	$ (71,479)	$ (78,161)
LOSS PER SHARE:
Basic and diluted (in dollars per share)	$ (2.56)	$ (4.04)	$ (203.91)
WEIGHTED AVERAGE SHARES:
Basic and diluted (in shares)	39,643,099	17,699,487	383,310