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DEFERRED COMPENSATION LIABILITY (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Post Retirement Benefits With Individual Employees [Line Items]
Total expense recognized	$ 1,391	$ 1,741	$ 2,450
Executive Vice President and Chief Financial Officer [Member]
Post Retirement Benefits With Individual Employees [Line Items]
Required service period (in years)	20.5Y
Maximum benefit as a percentage of salary (in hundredths)	66.00%
Retirement age (in years)	67
Imputed interest rate (in hundredths)	3.90%	3.90%
Chairman, President and CEO [Member]
Post Retirement Benefits With Individual Employees [Line Items]
Required service period (in years)	14Y
Maximum benefit as a percentage of salary (in hundredths)	66.00%
Retirement age (in years)	70
Imputed interest rate (in hundredths)	3.90%	3.90%

X

- Definition

The imputed interest on benefit plan assets.

+ References

No definition available.

+ Details

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Namespace Prefix:	nat_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The maximum annual benefit as a percentage of salary at the time of retirement.

+ References

No definition available.

+ Details

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Namespace Prefix:	nat_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The required retirement age of plan participants.

+ References

No definition available.

+ Details

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

X

- Details

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Balance Type:	na
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X

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 710

-SubTopic 10

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363



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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 6, 7

-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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

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X

- Definition

The minimum period that the individual is required to perform services in order to be fully vested under the deferred compensation arrangement.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-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 Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65, A240

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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