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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Vessels (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2021 USD ($)
Vessels [Abstract] |
Estimate useful life of vessel | 25 years
Market rates for the initial period | 2 years
Historical and average spot market rate | 15 years
Long-term residual value of the vessel | $ 8.0
Ballast Tank [Member] |
Vessels [Abstract] |
Improvements amortized over a period | 8 years

X
- Definition Period over which improvements are amortized, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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Balance Type: | na
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X
- Definition The historical and average spot market rate used when estimating daily time charter equivalent for the remaining operating days, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | nat_HistoricalAndAverageSpotMarketRate
Namespace Prefix: | nat_
Data Type: | xbrli:durationItemType
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Period Type: | duration

X
- Definition Market rates for the initial period used when estimating daily time charter equivalent for the remaining operating days, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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Namespace Prefix: | nat_
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Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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X
- Definition The estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose). + References No definition available. + Details
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X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |