| Share-Based Compensation - Summary of Share-based Compensation Expense (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | |
| Research and Development Expense | ||||
| Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] | ||||
| Share-based compensation expense | $ 189 | $ 83 | $ 548 | $ 280 | 
| General and Administrative Expense | ||||
| Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] | ||||
| Share-based compensation expense | $ 372 | $ 391 | $ 1,126 | $ 598 | 
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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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