SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Research and development and advertising costs, Government grants, Capitalized interest and Debt issuance cost (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Research and development and advertising costs
Research and development expenses	¥ 39,343	¥ 40,049	¥ 21,627
Advertising costs	15,043	14,778	7,454
Government grants
Deferred government grants in other long-term liabilities	22,245	6,196
Capitalized interest
Total interest costs	1,805,434	1,402,015	1,040,898
Less: interest costs capitalized	(150,697)	(85,509)	(72,205)
Interest expenses	1,654,737	1,316,506	¥ 968,693
Debt issuance costs
Unamortised debt issuance costs	197,119	226,085
Noncurrent liabilities
Government grants
Deferred government grants in other long-term liabilities	22,245	6,196
Other current assets
Debt issuance costs
Unamortized debt commitment costs	¥ 0	¥ 28,919

Deferred Debt Commitment Costs

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Carrying amount due after one year of the balance sheet date (or one operating cycle, if longer) of amounts deferred under the terms of governmental, corporate, or foundation grants.

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Represents information pertaining to research and development and advertising costs.

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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.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of interest costs capitalized disclosed as an adjusting item to interest costs incurred.

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Total interest costs incurred during the period and either capitalized or charged against earnings.

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Amount of the cost of borrowed funds accounted for as interest expense.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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