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Prepaid Expenses and Other Current Assets - Prepaid Expenses and Other Current Assets (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]    
Prepaid expenses $ 3,592 $ 4,717
Deposits 61 66
Interest receivable on marketable securities 560 717
Total prepaid expenses and other current assets $ 4,213 $ 5,500