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Significant Accounting Policies - Assets and Liability Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Asset:    
Cash equivalents—money markets $ 9,995 $ 9,880
Level 1    
Asset:    
Cash equivalents—money markets $ 9,995 $ 9,880