Commitments and Contingencies - Additional Information (Detail) - USD ($) |
12 Months Ended | |
|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Commitments And Contingencies Disclosure [Abstract] | ||
| Lease expiration term | Jun. 30, 2027 | |
| Rent expense | $ 2,033,000 | $ 1,300,000 |
| Eligibility for 401(k) retirement savings plan | 90 days | |
| 401(k) retirement savings plan matching contributions | $ 0 | |
| Defined Contribution Plan, Sponsor Location [Extensible List] | us-gaap:DomesticPlanMember | |