Summary of Significant Accounting Policies - Property and Equipment, Net (Details) |
12 Months Ended |
|---|---|
Dec. 31, 2019 | |
| Property and equipment, net | |
| Leasehold improvements | The shorter of lease terms and estimated useful lives |
| Building | |
| Property and equipment, net | |
| Useful lives | 30 years |
| Computer equipment | Minimum | |
| Property and equipment, net | |
| Useful lives | 3 years |
| Computer equipment | Maximum | |
| Property and equipment, net | |
| Useful lives | 5 years |
| Furniture, fixtures and office equipment | |
| Property and equipment, net | |
| Useful lives | 5 years |
| Software | Minimum | |
| Property and equipment, net | |
| Useful lives | 3 years |
| Software | Maximum | |
| Property and equipment, net | |
| Useful lives | 5 years |
| Motor vehicles | |
| Property and equipment, net | |
| Useful lives | 5 years |