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Research Collaboration Agreement and License Agreement (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Research Collaboration Agreement and License Agreement (Textual)              
Research and development expenses $ 1,018 $ 1,597 $ 4,292 $ 5,645 $ 7,349 $ 6,042 $ 9,028
Harvard License Agreement and Collaboration Agreement [Member]              
Research Collaboration Agreement and License Agreement (Textual)              
Total payment obligation     7,200   6,500    
Research and development expenses $ 252   $ 1,364   $ 900    
Research collaboration agreement expire date     May 16, 2022   May 16, 2021