Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
OPERATING EXPENSES:
Research and development	$ 26,891	$ 16,278	$ 54,374	$ 27,837
General and administrative	17,193	6,000	30,839	10,756
Loss from operations	(44,084)	(22,278)	(85,213)	(38,593)
OTHER (EXPENSE) INCOME:
Other (expense) income, net	(95)	(78)	(96)	(128)
Interest income	744	185	1,411	290
Interest expense	0	(794)	0	(1,591)
NET LOSS	(43,435)	(22,965)	(83,898)	(40,022)
OTHER COMPREHENSIVE LOSS, NET OF TAX:
Unrealized (loss) gain from available-for-sale securities	(49)	(31)	183	31
COMPREHENSIVE LOSS	(43,484)	(22,996)	(83,715)	(39,991)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED (Note 10)	$ (43,435)	$ (22,965)	$ (83,898)	$ (40,022)
LOSS PER SHARE:
Basic and diluted (in dollars per share)	$ (1.01)	$ (0.61)	$ (1.95)	$ (1.08)
WEIGHTED AVERAGE SHARES:
Basic and diluted (in shares)	43,042,883	37,895,651	43,027,903	37,089,642