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Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
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Payables And Accruals [Abstract] |  |
Employee benefits | $ 530 | $ 442
Legal expense | 388 | 343
Professional services | 256 | 88
Advance from U.S Army | 233 | 233
Deferred rent | 104 | 97
Severance |  | 38
Other | 1 | 1
Total accrued expenses | $ 1,512 | $ 1,242

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