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INCOME TAX - Movement of the valuation allowance (Details) - CNY (¥) ¥ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Movement of the valuation allowance |  |  |
Balance at the beginning of the year | ¥ 205,976 | ¥ 155,852 | ¥ 152,241
Increase during the year | 122,845 | 50,124 | 3,611
Balance at the end of the year | ¥ 328,821 | ¥ 205,976 | ¥ 155,852

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- References No definition available. + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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