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]
R&D tax credit receivable	$ 1,236	$ 1,263
Prepaid clinical trial costs	510	561
VAT receivable	311	421
Prepaid insurance	121	162
Deposits and other	161	107
Total prepaid expenses and other current assets	$ 2,339	$ 2,514