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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Cash, Cash Equivalents and Restricted Cash (Details)	12 Months Ended
	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