SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Goodwill (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Impairment losses for goodwill	¥ 0	¥ 0	¥ 0

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
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