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Refers to be number of new buildings.

No definition available.

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Data Type:	xbrli:integerItemType
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The number of vessels the company has taken through periodical maintenance survey as of the balance sheet date.

No definition available.

Name:	nat_NumberOfVesselsTakenThroughPeriodicalMaintenanceSurvey
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The percentage of remaining installments due in due in the second fiscal year following the latest fiscal year.

No definition available.

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Data Type:	num:percentItemType
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The percentage of remaining installments due in next fiscal year following the latest fiscal year.

No definition available.

Name:	nat_PercentageOfRemainingInstallmentsDueNextTwelveMonths
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Data Type:	num:percentItemType
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Amount before accumulated depreciation of vessels used in the normal conduct of business and not intended for resale.

No definition available.

Name:	nat_VesselsGross
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Carrying amount at the balance sheet date of vessels used in the normal conduct of business and not intended for resale, net of accumulated depreciation on vessels.

No definition available.

Name:	nat_VesselsNet
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Carrying amount at the balance sheet date of vessels under construction.

No definition available.

Name:	nat_VesselsUnderConstruction
Namespace Prefix:	nat_
Data Type:	xbrli:monetaryItemType
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The number of vessels under the operational management at of the balance sheet date.

No definition available.

Name:	nat_VesselsUnderOperations
Namespace Prefix:	nat_
Data Type:	xbrli:integerItemType
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Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References

No definition available.

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Amount of acquisition of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentAdditions
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Data Type:	xbrli:monetaryItemType
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Amount of divestiture of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentDisposals
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- References

No definition available.

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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