Note 21 - Selected Quarterly Data (Unaudited) (Details) - Quarterly Data (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Quarterly Data [Abstract]                      
Revenue $ 303,453 $ 398,615 $ 473,163 $ 798,788 $ 715,747 $ 981,247 $ 1,263,008 $ 1,461,687 $ 1,974,019 $ 4,421,689 $ 7,039,010
Research and development 13,459,178 12,998,409 10,569,134 8,472,195 7,069,151 5,630,219 6,102,320 5,189,461 45,498,916 23,991,151 17,616,892
General and administrative 2,480,025 2,320,036 1,865,822 1,933,476 1,620,068 1,024,167 939,725 1,078,357 8,599,359 4,662,317 6,135,581
Operating loss (15,635,750) (14,919,830) (11,961,793) (9,606,883) (7,973,472) (5,673,139) (5,779,037) (4,806,131) (52,124,256) (24,231,779) (16,713,463)
Other income (expense), net (584,660) (181,187) (21,738) (394,097) (47,450) 541 196 356,929      
Net loss (16,220,410) (15,101,017) (11,983,531) (10,000,980) (8,020,922) (5,672,598) (5,778,841) (4,449,202) (53,305,938) (23,921,563) (10,471,330)
Accretion of redeemable convertible preferred stock       (863,226) (477,029) 5,325,406 (10,446) (64,940) (863,226) 4,772,991 (351,371)
Less: Preferred stock dividend due to exchanges of preferred shares           (14,726,088)       (14,726,088)  
Net loss attributable to common stockholders $ (16,220,410) $ (15,101,017) $ (11,983,531) $ (10,864,206) $ (8,497,951) $ (15,073,280) $ (5,789,287) $ (4,514,142) $ (54,169,164) $ (33,874,660) $ (10,822,701)
Net loss attributable to common stockholders per share, basic and diluted (in Dollars per share) $ (0.83) $ (0.77) $ (0.61) $ (1.05) $ (36.19) $ (65.23) $ (25.53) $ (19.91) $ (3.12) $ (147.37) $ (54.58)
Weighted average shares outstanding, basic and diluted (in Shares) 19,656,209 19,655,561 19,655,187 10,376,561 234,789 231,084 226,757 226,757 17,367,665 229,865 198,306