LOSS PER ORDINARY SHARE - Excluded from the computation of diluted loss per share (Details) - shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive securities excluded from computation of earnings per share
Total	77,951,817	94,513,992	100,817,536
Share options/restricted shares
Antidilutive securities excluded from computation of earnings per share
Total	31,425,768	47,986,392	54,289,936
Convertible bonds payable
Antidilutive securities excluded from computation of earnings per share
Total	46,526,049	46,527,600	46,527,600

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration