| Schedule of Quarterly Financial Information | 
 The operating results for any quarter
are not necessarily indicative of results for any future period. 
  
    |   | 
      | 
    Quarters Ended | 
      | 
 
    |   | 
      | 
    December 31, 
2019 | 
      | 
      | 
    September 30, 
2019 | 
      | 
      | 
    June 30, 
2019 | 
      | 
      | 
    March 31, 
2019 | 
      | 
 
    | Foundation revenues | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
      | 
    $ | 
    - | 
      | 
 
    | Royalties | 
      | 
      | 
    - | 
      | 
      | 
      | 
    - | 
      | 
      | 
      | 
    - | 
      | 
      | 
      | 
    - | 
      | 
 
    | Research and development | 
      | 
      | 
    9,605,000 | 
      | 
      | 
      | 
    10,917,000 | 
      | 
      | 
      | 
    16,307,000 | 
      | 
      | 
      | 
    11,737,000 | 
      | 
 
    | General and administrative | 
      | 
      | 
    4,734,000 | 
      | 
      | 
      | 
    4,700,000 | 
      | 
      | 
      | 
    5,612,000 | 
      | 
      | 
      | 
    5,659,000 | 
      | 
 
    | Loss from operations | 
      | 
      | 
    (16,411,000 | 
    ) | 
      | 
      | 
    (17,649,000 | 
    ) | 
      | 
      | 
    (23,976,000 | 
    ) | 
      | 
      | 
    (19,054,000 | 
    ) | 
 
    | Net loss | 
      | 
      | 
    (16,431,000 | 
    ) | 
      | 
      | 
    (17,372,000 | 
    ) | 
      | 
      | 
    (23,924,000 | 
    ) | 
      | 
      | 
    (18,555,000 | 
    ) | 
 
    | Basic and diluted loss per common share | 
      | 
      | 
    (0.30 | 
    ) | 
      | 
      | 
    (0.35 | 
    ) | 
      | 
      | 
    (0.49 | 
    ) | 
      | 
      | 
    (0.39 | 
    ) | 
 
    | Weighted average number of common shares outstanding – basic and diluted | 
      | 
      | 
    54,718,776 | 
      | 
      | 
      | 
    49,721,753 | 
      | 
      | 
      | 
    48,961,988 | 
      | 
      | 
      | 
    47,948,421 | 
      | 
 
 
  
    |   | 
      | 
    Quarters Ended | 
      | 
      | 
 
    |   | 
      | 
      | 
    December 31, 
2018 | 
      | 
      | 
      | 
    September 30, 
2018 | 
      | 
      | 
      | 
    June 30, 
2018 | 
      | 
      | 
      | 
    March 31, 
2018 | 
      | 
 
    | Foundation revenues | 
      | 
    $ | 
    369,000 | 
      | 
      | 
    $ | 
    1,687,000 | 
      | 
      | 
    $ | 
    259,000 | 
      | 
      | 
    $ | 
    481,000 | 
      | 
 
    | Royalties | 
      | 
      | 
    113,000 | 
      | 
      | 
      | 
    22,000 | 
      | 
      | 
      | 
    17,000 | 
      | 
      | 
      | 
    50,000 | 
      | 
 
    | Research and development | 
      | 
      | 
    9,470,000 | 
      | 
      | 
      | 
    13,150,000 | 
      | 
      | 
      | 
    7,916,000 | 
      | 
      | 
      | 
    8,162,000 | 
      | 
 
    | General and administrative | 
      | 
      | 
    7,631,000 | 
      | 
      | 
      | 
    4,970,000 | 
      | 
      | 
      | 
    4,627,000 | 
      | 
      | 
      | 
    2,878,000 | 
      | 
 
    | Loss from operations | 
      | 
      | 
    (18,010,000 | 
    ) | 
      | 
      | 
    (16,916,000 | 
    ) | 
      | 
      | 
    (12,557,000 | 
    ) | 
      | 
      | 
    (10,683,000 | 
    ) | 
 
    | Net loss | 
      | 
      | 
    (17,479,000 | 
    ) | 
      | 
      | 
    (16,419,000 | 
    ) | 
      | 
      | 
    (12,243,000 | 
    ) | 
      | 
      | 
    (10,530,000 | 
    ) | 
 
    | Basic and diluted loss per common share | 
      | 
      | 
    (0.36 | 
    ) | 
      | 
      | 
    (0.34 | 
    ) | 
      | 
      | 
    (0.26 | 
    ) | 
      | 
      | 
    (0.22 | 
    ) | 
 
    | Weighted average number of common shares outstanding – basic and diluted | 
      | 
      | 
    47,944,486 | 
      | 
      | 
      | 
    47,794,394 | 
      | 
      | 
      | 
    47,303,518 | 
      | 
      | 
      | 
    47,060,523 | 
      | 
 
 
 |