SUMMARY OF PRINCIPAL ACCOUNTING POLICIES - Concentration of credit risk (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Concentration of credit risk
Advances to suppliers	$ 225,879	$ 182,146
Supplier \| Supplier A
Concentration of credit risk
Advances to suppliers	52,257	$ 43,821
Supplier \| Supplier B
Concentration of credit risk
Advances to suppliers	37,117
Supplier \| Supplier C
Concentration of credit risk
Advances to suppliers	$ 36,026

Carrying value of capitalized payments made in advance for inventory that is expected to be received within one year or the normal operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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