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	Mar. 31, 2019 USD ($)
Operating Lease Liabilities, Payments Due [Abstract]
2019 (Excluding the three months ended March 31, 2019)	$ 915
2020	1,239
2021	1,264
2022	1,288
2023	1,164
Total future minimum lease payments, undiscounted	5,870
Less imputed interest	(882)
Operating lease liability	4,988
Operating lease liability reported as of March 31, 2019:
Operating lease liability-current	901
Operating lease liability - non-current	4,087
Total	$ 4,988