Condensed Consolidated Statements of Operations (Unaudited) (USD $)
In Thousands, except Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Income Statement [Abstract]        
Revenue $ 2,459 $ 2,777 $ 4,024 $ 4,265
Operating expenses:        
Research and development 6,901 5,960 13,724 11,617
General and administrative 3,774 2,449 7,035 4,416
Total operating expenses 10,675 8,409 20,759 16,033
Loss from operations (8,216) (5,632) (16,735) (11,768)
Other income (expense)        
Interest expense, net (72) (51) (156) (104)
Other income (expense), net (156) (236) 125 (336)
Total other income (expense) (228) (287) (31) (440)
Net loss (8,444) (5,919) (16,766) (12,208)
Accretion of redeemable convertible preferred stock   (1,412)   (2,749)
Net loss attributable to common stockholders $ (8,444) $ (7,331) $ (16,766) $ (14,957)
Net loss per share attributable to common stockholders:        
Basic and diluted $ (0.51) $ (3.32) $ (1.02) $ (6.83)
Weighted average common shares outstanding:        
Basic and diluted 16,464,410 2,210,766 16,444,210 2,190,479