RELATED PARTY TRANSACTIONS - Balances with Major related parties (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2020 CNY (¥)	Dec. 31, 2019 CNY (¥)
Current assets:
Total	$ 99,056	¥ 646,341	¥ 308,682
Due to Related Parties, Current [Abstract]
Total	$ 8,110	52,918	82,800
JD Group
Current assets:
Total		562,194	236,196
Due to Related Parties, Current [Abstract]
Total		26,545	19,350
Walmart group
Current assets:
Total		84,147	72,486
Due to Related Parties, Current [Abstract]
Total		¥ 26,373	¥ 63,450

The aggregate amount of receivables to be collected from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth, at the financial statement date. which are usually due within one year (or one business cycle).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
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-Name Accounting Standards Codification
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Name:	us-gaap_DueFromRelatedPartiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant