Condensed Statements of Operations and Comprehensive Loss (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
OPERATING EXPENSES:      
Research and development $ 45,719 $ 60,536 $ 54,961
General and administrative 13,674 6,829 9,469
Loss from operations (59,393) (67,365) (64,430)
OTHER (EXPENSE) INCOME:      
Other (expense) income, net (510) 9,085 (2,095)
Loss on retirement of note payable (203)    
Interest income 94 30 64
Interest expense (2,467) (2,440) (2,667)
NET LOSS (62,479) (60,690) (69,128)
OTHER COMPREHENSIVE LOSS, NET OF TAX:      
Unrealized loss from available-for-sale securities (21)   (5)
COMPREHENSIVE LOSS (62,500) (60,690) (69,133)
LOSS ATTRIBUTABLE TO COMMON STOCKHOLDERS - BASIC AND DILUTED (Note 12) $ (71,479) $ (78,161) $ (83,120)
LOSS PER SHARE:      
Basic and diluted (in dollars per share) $ (4.04) $ (203.91) $ (225.71)
WEIGHTED AVERAGE SHARES:      
Basic and diluted (in shares) 17,699,487 383,310 368,261