SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Employee benefit expenses and Segment reporting (Details) ¥ in Millions, $ in Millions	12 Months Ended
Dec. 31, 2025 CNY (¥) segment	Dec. 31, 2025 USD ($) segment	Dec. 31, 2024 CNY (¥)	Dec. 31, 2023 CNY (¥)
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Employee benefit expenses	¥ 1,151.7	$ 164.4	¥ 864.0	¥ 530.3
Number of reportable segments	1	1

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-47

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 54
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-54

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-18

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