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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Cash, Cash Equivalents and Restricted Cash (Details) | 12 Months Ended
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Dec. 31, 2021
Cash, Cash Equivalents and Restricted Cash [Abstract] |
Original maturities of deposits classified as cash and cash equivalents | 3 months

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- Definition The original maturity, in months, of deposits classified as cash and cash equivalents, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | nat_OriginalMaturitiesOfDepositsClassifiedAsCashAndCashEquivalents
Namespace Prefix: | nat_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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