RESTRICTED NET ASSETS (Details) ¥ in Thousands	12 Months Ended
Dec. 31, 2020 CNY (¥)	Dec. 31, 2019 CNY (¥)
RESTRICTED NET ASSETS
Appropriation of after-tax income to statutory surplus reserve fund (as a percentage)	10
Threshold percentage of after-tax income required to be appropriated towards reserve until the reserve balance reaches a specified percentage of registered capital.	50
Restricted net assets	¥ 8,612,691	¥ 7,317,215

Amount of restricted net assets of consolidated and unconsolidated subsidiaries as of the end of the most recently completed fiscal year.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e)(3)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Name:	us-gaap_AmountOfRestrictedNetAssetsForConsolidatedAndUnconsolidatedSubsidiaries
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant