Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
OPERATING EXPENSES:
Research and development	$ 19,527	$ 27,483
General and administrative	38,099	13,646
Loss from operations	(57,626)	(41,129)
OTHER (EXPENSE) INCOME:
Other (expense) income, net	80	(1)
Interest income	607	667
NET LOSS	(56,939)	(40,463)
OTHER COMPREHENSIVE LOSS, NET OF TAX:
Unrealized (loss) gain from available-for-sale securities	(37)	232
COMPREHENSIVE LOSS	(56,976)	(40,231)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED (Note 10)	$ (56,939)	$ (40,463)
LOSS PER SHARE:
Basic and diluted (in dollars per share)	$ (1.32)	$ (0.94)
WEIGHTED AVERAGE SHARES:
Basic and diluted (in shares)	43,185,952	43,012,924