Consolidated Balance Sheets (USD $)
Dec. 31, 2014
Dec. 31, 2013
Current assets    
Cash and cash equivalents $ 37,223,590 $ 33,297,970
Short-term investments 19,016,347 13,659,812
Prepaid expenses 838,420 629,935
Deferred financing costs 309,927 1,516,424
Other receivables 129,019 424,501
Total current assets 57,517,303 49,528,642
Property and equipment, net 5,513,555 1,602,103
Restricted cash 1,325,000  
Other assets 11,020 550
Total assets 64,366,878 51,131,295
Current liabilities    
Accounts payable 1,860,491 1,317,072
Other accrued expenses 1,405,378 1,800,794
Current portion of notes payable 30,885 45,447
Total current liabilities 3,296,754 3,163,313
Long-term portion of notes payable 19,796,545 7,014,106
Long-term portion of manufacturing research and development obligation 3,475,552  
Long-term portion of facility lease obligation 3,380,223  
Deferred liability 3,066,000 3,066,000
Commitments      
Stockholders’ (deficit) equity    
Preferred stock $0.001 par value; 0 and 5,000,000 shares authorized as of December 31, 2013 and 2014; 0 shares issued and outstanding as of December 31, 2013 and 2014      
Common stock $0.001 par value; 120,000,000 and 200,000,000 shares authorized as of December 31, 2013 and 2014; 235,707 and 19,657,412 shares issued and outstanding as of December 31, 2013 and 2014 19,657 236
Accumulated other comprehensive loss (124,841) (102,531)
Additional paid-in capital 235,627,174 75,189,950
Accumulated deficit (204,170,186) (150,864,248)
Total stockholders’ (deficit) equity 31,351,804 (75,776,593)
Total liabilities, redeemable convertible preferred stock and stockholders’ (deficit) equity 64,366,878 51,131,295
Series A Preferred Stock [Member]    
Current liabilities    
Temporary stock   332,869
Series B Preferred Stock [Member]    
Current liabilities    
Temporary stock   5,521,437
Series C Preferred Stock [Member]    
Current liabilities    
Temporary stock   2,655,884
Series D Preferred Stock [Member]    
Current liabilities    
Temporary stock   33,262,492
Series E Preferred Stock [Member]    
Current liabilities    
Temporary stock   $ 71,891,787