Commitments and Contingencies - Schedule of Future Minimum Lease Payments under Non-cancellable Operating Leases, Reconciliation of Undiscounted Cash Flows to the Operating Lease Liability (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Operating Lease Liabilities, Payments Due [Abstract]
2019 (Excluding the six months ended June 30, 2019)	$ 613
2020	1,239
2021	1,264
2022	1,288
2023	1,164
Total future minimum lease payments, undiscounted	5,568
Less imputed interest	(796)
Operating lease liability	4,772
Operating lease liability reported as of June 30, 2019:
Operating lease liability - current	923
Operating lease liability - non-current	3,849
Total	$ 4,772