Revenue from transporting cargo and freight between locations under gross revenue method.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Revenue from transporting cargo and freight between locations where voyage revenues and voyage expenses are presented gross in the statements of operations.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Revenue from transporting cargo and freight between locations under net revenue method.

+ References

No definition available.

+ Details

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

- Definition

Represents to number of charters.

+ References

No definition available.

+ Details

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

- Definition

Represents to number of customers.

+ References

No definition available.

+ Details

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Namespace Prefix:	nat_
Data Type:	xbrli:integerItemType
Balance Type:	na
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- Details

Name:	nat_RevenueAbstract
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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Revenue from transporting cargo and freight between locations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(d))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Balance Type:	na
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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

+ Details

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Period Type:	duration

- Definition

The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph a

-Article 5

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 210.5-02.3,4)

-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 4

-Article 5

+ Details

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

- Details

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- Details

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REVENUE (Details) (USD $)	12 Months Ended
REVENUE (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
REVENUE [Abstract]
Net pool spot market earnings, cooperative arrangements	$ 0nat_NetMethodRevenue	$ 0nat_NetMethodRevenue	$ 77,287,000nat_NetMethodRevenue
Gross pool spot market earnings, Orion Tankers pool	0nat_GrossPoolMethodRevenue	0nat_GrossPoolMethodRevenue	36,339,000nat_GrossPoolMethodRevenue
Gross spot market earnings, through spot charters	351,049,000nat_GrossMethodRevenue	243,657,000nat_GrossMethodRevenue	17,056,000nat_GrossMethodRevenue
Total Voyage Revenues	351,049,000us-gaap_CargoAndFreightRevenue	243,657,000us-gaap_CargoAndFreightRevenue	130,682,000us-gaap_CargoAndFreightRevenue
Concentration Risk [Line Items]
Accounts receivable	$ 16,400,000us-gaap_ReceivablesNetCurrent	$ 18,800,000us-gaap_ReceivablesNetCurrent
Voyage Revenues [Member] \| Gemini Tankers LLC [Member]
Concentration Risk [Line Items]
Concentration risk, percentage (in hundredths)			2.00%
Voyage Revenues [Member] \| Orion Tankers Pool [Member]
Concentration Risk [Line Items]
Concentration risk, percentage (in hundredths)			98.00%
Voyage Revenues [Member] \| XX Customers [Member]
Concentration Risk [Line Items]
Concentration risk, percentage (in hundredths)	40.00%
Number of customers	2
Voyage Revenues [Member] \| Two Customers [Member]
Concentration Risk [Line Items]
Concentration risk, percentage (in hundredths)		42.00%
Number of customers		2
Accounts Receivable [Member] \| Three Charters [Member]
Concentration Risk [Line Items]
Concentration risk, percentage (in hundredths)	62.00%
Number of charters	3
Accounts Receivable [Member] \| Four Charters [Member]
Concentration Risk [Line Items]
Concentration risk, percentage (in hundredths)		52.00%
Number of charters		4