SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Sales and marketing expenses and General and administrative expenses ,Income taxes (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2025 CNY (¥)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 CNY (¥)	Dec. 31, 2023 CNY (¥)
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Delivery expenses	¥ 6,878,700	$ 981,800	¥ 2,821,069	¥ 2,010,699
Sales and marketing expenses
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Advertising expenditure	1,293,200	184,600	1,206,400	801,100
General and administrative expenses
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Research and development costs	¥ 612,600	$ 87,400	¥ 493,800	¥ 338,800

Amount of costs of deliveries made to customers for the period.

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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.

+ References

No definition available.

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- Definition

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition

Amount of expense for research and development. Includes, but is not limited to, cost for computer software product to be sold, leased, or otherwise marketed and writeoff of research and development assets acquired in transaction other than business combination or joint venture formation or both. Excludes write-down of intangible asset acquired in business combination or from joint venture formation or both, used in research and development activity.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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