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Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Payables And Accruals [Abstract]    
Accounts payable $ 4,943 $ 4,371
Accrued research projects 6,446 6,079
Accrued professional fees 721 802
Accrued compensation and benefits 1,200 2,370
Total $ 13,310 $ 13,622