XML 42 R45.htm IDEA: XBRL DOCUMENT v2.4.1.9

VESSELS, NET (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012 Vessel	Dec. 31, 2014 Vessel	Dec. 31, 2013 Vessel	Dec. 31, 2012
VESSELS, NET [Abstract]
Number of vessels		22nat_VesselsUnderOperations	20nat_VesselsUnderOperations
Number of vessels the Company believed had future undiscounted cash flow less than carrying value	1nat_NumberOfVesselsHavingFutureUndiscountedCashFlowLessThanCarryingValue
Impairment loss on vessel		$ 0us-gaap_AssetImpairmentCharges	$ 0us-gaap_AssetImpairmentCharges	$ 12,030us-gaap_AssetImpairmentCharges
Schedule of Vessels [Line Items]
Carrying Value		909,992nat_VesselsNet	911,429nat_VesselsNet
Accumulated Depreciation		567,645us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	487,485us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
Depreciation Expense		80,160nat_DepreciationVesselsOnly	74,022nat_DepreciationVesselsOnly
Acquisition of vessels		73,904nat_VesselsAcquired
Vessels [Member]
Schedule of Vessels [Line Items]
Carrying Value		882,221nat_VesselsNet / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember	872,846nat_VesselsNet / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember
Accumulated Depreciation		524,651us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember	460,422us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember
Depreciation Expense		64,229nat_DepreciationVesselsOnly / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember	62,781nat_DepreciationVesselsOnly / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember
Acquisition of vessels		73,604nat_VesselsAcquired / nat_PropertyByVesselOrOtherEquipmentAxis = nat_VesselsMember
Drydocking [Member]
Schedule of Vessels [Line Items]
Carrying Value		27,771nat_VesselsNet / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember	38,583nat_VesselsNet / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember
Accumulated Depreciation		42,994us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember	27,063us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember
Depreciation Expense		15,931nat_DepreciationVesselsOnly / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember	11,241nat_DepreciationVesselsOnly / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember
Acquisition of vessels		$ 300nat_VesselsAcquired / nat_PropertyByVesselOrOtherEquipmentAxis = nat_DrydockingMember

X

- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of vessels over the assets' useful lives.

+ References

No definition available.

+ Details

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

X

- Definition

The number of vessels the Company believed had future undiscounted cash flow less than the carrying value and therefore not fully recoverable.

+ References

No definition available.

+ Details

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X

- Details

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Namespace Prefix:	nat_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The total value of vessels acquired during period.

+ References

No definition available.

+ Details

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Namespace Prefix:	nat_
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Balance Type:	debit
Period Type:	instant

X

- Definition

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.

+ References

No definition available.

+ Details

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Namespace Prefix:	nat_
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- Details

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X

- Definition

The number of vessels under the operational management at of the balance sheet date.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.14)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 14

-Article 5

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X

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585



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

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-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228

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