Condensed Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
OPERATING EXPENSES:
Research and development	$ 16,240	$ 14,499	$ 33,527	$ 24,366
General and administrative	1,444	2,179	3,022	4,291
Loss from operations	(17,684)	(16,678)	(36,549)	(28,657)
OTHER (EXPENSE) INCOME:
Other (expense) income, net	(1,184)	(717)	10,072	(1,184)
Interest income	14	18	16	35
Interest expense	(658)	(584)	(1,356)	(1,027)
NET LOSS	(19,512)	(17,961)	(27,817)	(30,833)
OTHER COMPREHENSIVE LOSS, NET OF TAX:
Unrealized gain from available-for-sale securities	3	6	3	5
COMPREHENSIVE LOSS	(19,509)	(17,955)	(27,814)	(30,828)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED (Note 10):	$ (23,880)	$ (21,417)	$ (35,767)	$ (37,643)
LOSS PER SHARE:
Basic (in dollars per share)	$ (27.45)	$ (25.06)	$ (41.18)	$ (46.18)
Diluted (in dollars per share)	$ (27.45)	$ (25.06)	$ (41.18)	$ (46.18)
WEIGHTED AVERAGE SHARES:
Basic (in shares)	869,878	854,517	868,548	815,053
Diluted (in shares)	869,878	854,517	868,548	815,053