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Strategic Alliance with Allseas and Affiliates - Exclusive Vessel Use Agreement with Allseas (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
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Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024 | Dec. 31, 2024
Strategic Alliance with Allseas and Affiliates |  |  |  |  |
Lease expense | $ 500 | $ 500 | $ 954 | $ 954 | $ 1,907

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- Definition The entire disclosure about strategic partnerships. + References No definition available. + Details
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Namespace Prefix: | tmc_
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- Definition Amount of operating lease expense. Excludes sublease income. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-4 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration