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Taxation - Movement of the aggregate valuation allowances for deferred tax assets (Details) - CNY (¥) ¥ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Deferred Tax Asset Valuation Allowance [Roll Forward] |  |  |
Balance at January 1 | ¥ (89,713) | ¥ (62,714) | ¥ (48,555)
Addition | (30,990) | (26,999) | (14,159)
Balance at December 31 | ¥ (120,703) | ¥ (89,713) | ¥ (62,714)

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- Definition Deferred Tax Asset Valuation Allowance [Roll Forward]. + References No definition available. + Details
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Namespace Prefix: | tc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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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
Name: | us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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