Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
OPERATING EXPENSES:
Research and development	$ 16,278	$ 10,618	$ 27,837	$ 20,335
General and administrative	6,000	3,070	10,756	5,209
Loss from operations	(22,278)	(13,688)	(38,593)	(25,544)
OTHER (EXPENSE) INCOME:
Other (expense) income, net	(78)	1,727	(128)	(506)
Loss on retirement of note payable		(203)		(203)
Interest income	185	5	290	7
Interest expense	(794)	(450)	(1,591)	(851)
NET LOSS	(22,965)	(12,609)	(40,022)	(27,097)
OTHER COMPREHENSIVE INCOME, NET OF TAX:
Unrealized (loss) gain from marketable securities	(31)	1	31	1
COMPREHENSIVE LOSS	(22,996)	(12,608)	(39,991)	(27,096)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED (Note 10)	$ (22,965)	$ (16,640)	$ (40,022)	$ (36,097)
LOSS PER SHARE:
Basic (in dollars per share)	$ (0.61)	$ (2.22)	$ (1.08)	$ (9.11)
Diluted (in dollars per share)	$ (0.61)	$ (2.22)	$ (1.08)	$ (9.11)
WEIGHTED AVERAGE SHARES:
Basic (in shares)	37,895,651	7,500,148	37,089,642	3,962,559
Diluted (in shares)	37,895,651	7,500,148	37,089,642	3,962,559