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Prepaid Expenses and Other Current Assets (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]    
Prepaid insurance $ 502 $ 437
Prepaid research and development 122 508
Other prepaid 597 321
Other current assets 388 298
Total $ 1,609 $ 1,564