XML 57 R39.htm IDEA: XBRL DOCUMENT v3.22.1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Vessels (Details) $ in Millions	12 Months Ended
	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

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

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
Balance Type:	na
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

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

X

- References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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

Name:	us-gaap_PropertyPlantAndEquipmentSalvageValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=nat_BallastTankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: