SUMMARY OF PRINCIPAL ACCOUNTING POLICIES - Property and equipment, net (Details) |
Dec. 31, 2025 |
|---|---|
| Leasehold improvements | |
| Property and equipment, net | |
| Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration] | us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember |
| Buildings | Minimum | |
| Property and equipment, net | |
| Property and equipment, estimated useful life | 20 years |
| Buildings | Maximum | |
| Property and equipment, net | |
| Property and equipment, estimated useful life | 40 years |
| Furniture, fixtures and equipment | Minimum | |
| Property and equipment, net | |
| Property and equipment, estimated useful life | 1 year |
| Furniture, fixtures and equipment | Maximum | |
| Property and equipment, net | |
| Property and equipment, estimated useful life | 20 years |
| Motor vehicles | |
| Property and equipment, net | |
| Property and equipment, estimated useful life | 5 years |