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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Drydocking (Details) | 12 Months Ended
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Dec. 31, 2021
Drydocking [Abstract] |
Period when vessels are required to be drydocked, minimum | 30 months
Period when vessels are required to be drydocked, maximum | 60 months

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- References No definition available. + Details
Name: | nat_DrydockAbstract
Namespace Prefix: | nat_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The maximum period when the vessels are expected to be drydocked for overhaul repairs and maintenance, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | nat_PeriodWhenVesselsAreRequiredToBeDrydockedMaximum
Namespace Prefix: | nat_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition The minimum period when the vessels are expected to be drydocked for overhaul repairs and maintenance, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | nat_PeriodWhenVesselsAreRequiredToBeDrydockedMinimum
Namespace Prefix: | nat_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration