SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Drydocking (Details)	12 Months Ended
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

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.

No definition available.

Name:	nat_PeriodWhenVesselsAreRequiredToBeDrydockedMaximum
Namespace Prefix:	nat_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration