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Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Payables And Accruals [Abstract]    
Accounts payable $ 2,485 $ 4,371
Accrued research projects 7,795 6,079
Accrued professional fees 527 802
Accrued compensation and benefits 1,959 2,370
Total $ 12,766 $ 13,622