Name:	nat_NumberOfVesselsCategorizedAsNewbuildings
Namespace Prefix:	nat_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The cash outflow associated with the construction of new vessels to be used in the normal conduct of business to produce services and not intended for resale.

No definition available.

Name:	nat_PaymentMadeToSellerOfVesselsCategorizedAsNewbuildings
Namespace Prefix:	nat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The percentage of purchase price paid upon signing of the contract related to acquisition of new vessels under construction to be used in the normal conduct of business and not intended for resale.

No definition available.

Name:	nat_PercentageOfPurchasePricesPaidRelatedToVesselsNewbuildings
Namespace Prefix:	nat_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The total number of vessels during the period, which may include crude oil tankers and new vessels under construction to be used in the normal conduct of business and not intended for resale.

No definition available.

Name:	nat_TotalNumberOfVessels
Namespace Prefix:	nat_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Agreed total price related to acquisition of new vessels under construction to be used in the normal conduct of business and not intended for resale.

No definition available.

Name:	nat_VesselsAgreedTotalPrice
Namespace Prefix:	nat_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

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).

No definition available.

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

The average useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLifeAverage
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

The amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 7

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25336-109308