Note 21 - Selected Quarterly Data (Unaudited)
12 Months Ended
Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]  
Quarterly Financial Information [Text Block]
21. Selected Quarterly Data (unaudited)

   
Quarter Ended
 
   
March 31,
2014
   
June 30,
2014
   
September 30,
2014
   
December 31,
2014
 
Revenue
  $ 798,788     $ 473,163     $ 398,615     $ 303,453  
Operating expenses:
                               
Research and development
    8,472,195       10,569,134       12,998,409       13,459,178  
General and administrative
    1,933,476       1,865,822       2,320,036       2,480,025  
                                 
Operating loss
    (9,606,883 )     (11,961,793 )     (14,919,830 )     (15,635,750 )
Other income (expense), net
    (394,097 )     (21,738 )     (181,187 )     (584,660 )
                                 
Net loss
    (10,000,980 )     (11,983,531 )     (15,101,017 )     (16,220,410 )
Accretion of redeemable convertible preferred stock
    (863,226 )                  
Less: Preferred stock dividend due to exchanges of preferred shares
    -       -       -       -  
                                 
Net loss attributable to common stockholders
  $ (10,864,206 )   $ (11,983,531 )   $ (15,101,017 )   $ (16,220,410 )
                                 
Net loss attributable to common stockholders per share, basic and diluted
  $ (1.05 )   $ (0.61 )   $ (0.77 )   $ (0.83 )
                                 
Weighted average shares outstanding, basic and diluted
    10,376,561       19,655,187       19,655,561       19,656,209  

   
Quarter Ended
 
   
March 31,
2013
   
June 30,
2013
   
September 30,
2013
   
December 31,
2013
 
Revenue
  $ 1,461,687     $ 1,263,008     $ 981,247     $ 715,747  
Operating expenses:
                               
Research and development
    5,189,461       6,102,320       5,630,219       7,069,151  
General and administrative
    1,078,357       939,725       1,024,167       1,620,068  
                                 
Operating loss
    (4,806,131 )     (5,779,037 )     (5,673,139 )     (7,973,472 )
Other income (expense), net
    356,929       196       541       (47,450 )
                                 
Net loss
    (4,449,202 )     (5,778,841 )     (5,672,598 )     (8,020,922 )
Accretion of redeemable convertible preferred stock
    (64,940 )     (10,446 )     5,325,406       (477,029 )
Less: Preferred stock dividend due to exchanges of preferred shares
                (14,726,088 )      
                                 
Net loss attributable to common stockholders
  $ (4,514,142 )   $ (5,789,287 )   $ (15,073,280 )   $ (8,497,951 )
                                 
Net loss attributable to common stockholders per share, basic and diluted
  $ (19.91 )   $ (25.53 )   $ (65.23 )   $ (36.19 )
                                 
Weighted average shares outstanding, basic and diluted
    226,757       226,757       231,084       234,789