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Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Prepaid Expense and Other Assets, Current [Abstract]    
Tax incentive refund $ 1,268 $ 1,325
Prepaid research and development costs 2,950 981
Prepaid insurance 227 316
Interest income receivable 200 220
Prepaid rent 83 81
Other current assets 475 795
Total $ 5,203 $ 3,718