Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Detail)

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Commitments and Contingencies - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Facilities Operating Leases          
Other Commitments [Line Items]          
Operating lease expense $ 304,000 $ 115,000 $ 644,000 $ 205,000  
Laboratory Equipment          
Other Commitments [Line Items]          
Property and equipment, gross 237,000   237,000   $ 162,000
Accumulated amortization $ 92,000   $ 92,000   $ 75,000