SUMMARY OF PRINCIPAL ACCOUNTING POLICIES - Revenue recognition - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Net revenues	$ 3,744,512	$ 3,390,393	$ 2,853,078
Recognized at a point in time \| Module
Disaggregation of Revenue [Line Items]
Net revenues	2,095,743	2,705,985	2,742,518
Recognized at a point in time \| Energy
Disaggregation of Revenue [Line Items]
Net revenues	1,542,906	633,195	25,755
Recognized over time \| Module
Disaggregation of Revenue [Line Items]
Net revenues	73,175	6,938	4,128
Recognized over time \| Energy
Disaggregation of Revenue [Line Items]
Net revenues	$ 32,688	$ 44,275	$ 80,677

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration