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COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011
COMMITMENTS AND CONTINGENCIES [Abstract] |
Legal fees of the Seller | $ 1.2

X
- Definition The estimated amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to the expenses incurred by the seller in regards to pending litigation. + References No definition available. + Details
Name: | nat_LegalFeesOfSeller
Namespace Prefix: | nat_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration