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Leases - Summary of lease cost (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Leases [Abstract]        
Operating lease cost $ 369 $ 213 $ 1,104 $ 582
Total lease cost 369 213 1,104 582
Cash paid for amounts included in the measurement of lease liabilities $ 218 $ 213 $ 874 $ 582