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Liquidity - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Liquidity [Abstract]    
Accumulated deficit $ 203,342 $ 173,494
Cash, cash equivalents and short-term investments 120,100  
Net loss 30,055 21,561
Cash used in operations $ 28,553 $ 19,940