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Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Mar. 31, 2019
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Organization and Financing              
Net loss $ (9,649) $ (15,666) $ (20,010) $ (22,488) $ (25,315) $ (42,498)  
Working capital 25,747       25,747    
Cash 20,040       20,040   $ 21,291
Accumulated deficit $ (155,223)       $ (155,223)   $ (130,240)