Restricted common shares subject to vesting that are allocated to persons employed in management of the entity.

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Number of warrants or rights vested.

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Factor defining the numbers of common shares the manager is entitled upon qualifying events (e.g. initial adoption of management agreement and subsequent share issues).

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The number of individual in management and Board members participating in incentive plan.

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Represents minimum business days required for exercise level.

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Represents minimum trading volume of exercise levels on balance sheet date.

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The total number of tankers withdrawn from pool during the period, which may include crude oil tankers and new vessels under construction to be used in the normal conduct of business and not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

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Represents percentage of common shares increase during the period.

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Represents percentages of increase in volume weighted average price during the period.

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New amount of management fee due to (decrease) increase during the period.

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Old amount of management fee before (decrease) increase during the period.

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Refers to the number of persons who got distributed the treasury stock.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Number of shares of equity interests issued or issuable to acquire entity.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Exercise price per share or per unit of warrants or rights outstanding.

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Number of warrants or rights outstanding.

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Costs of sales and operating expenses for the period incurred from transactions with related parties.

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Carrying amount as of the balance sheet date of obligations due all related parties. For classified balance sheets, represents the current portion of such liabilities (due within one year or within the normal operating cycle if longer).

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The amount of noncurrent assets reported by an equity method investment of the entity.

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Amount of dividend income on nonoperating securities.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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Gross number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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RELATED PARTY TRANSACTIONS (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended
RELATED PARTY TRANSACTIONS (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012 Tanker	Jan. 10, 2013	Jan. 31, 2014 Person	Dec. 31, 2012 Tanker	Dec. 31, 2011
Related Party Transaction [Line Items]
Costs and expenses, related party	$ 0us-gaap_CostsAndExpensesRelatedParty	$ 0us-gaap_CostsAndExpensesRelatedParty	$ 3,930,000us-gaap_CostsAndExpensesRelatedParty
Number of tankers withdrawn from pool			9nat_NumberOfTankersWithdrawnFromPool
Private equity placement issued amount	113,433,000	172,611,000	75,582,000
Investment in Nordic American Offshore Ltd	55,223,000	64,128,000
Dividend income recognized	252,000us-gaap_InvestmentIncomeDividend	0us-gaap_InvestmentIncomeDividend	0us-gaap_InvestmentIncomeDividend
Warrants received (in shares)	833,333	833,333
Warrants exercise price (n dollars per share)	$ 15.00	$ 15.00
Percentage of warrants vesting increments (in hundredths)	20.00%
Percentages of increase in volume weighted average price (in hundredths)	10.00%
Minimum business days required for exercise level of VWAP	10 days
VWAP minimum trading volume of exercise levels	2,000,000	2,000,000
Warrants vested (in shares)	333,333nat_ClassOfWarrantOrRightVested
Minimum [Member]
Related Party Transaction [Line Items]
Percentage of common shares increase (in hundredths)	25.00%	25.00%
Maximum [Member]
Related Party Transaction [Line Items]
Percentage of common shares increase (in hundredths)	65.00%	65.00%
Scandic American Shipping Ltd [Member]
Related Party Transaction [Line Items]
Manager's right to ownership of company's total outstanding shares (in hundredths)			2.00%
New amount of management fee due to decrease in the period		150,000,000
Previous amount of management fee before decrease in the period		500,000,000
Restricted shares authorized (in shares)							400,000
Individuals in management and board members participating in incentive plan	27		23
Allocated restricted common shares subject to vesting (in shares)	226,000
Restricted shares issued to the Manager (in shares)				174,000
Share-based compensation expense				1,100,000
Costs and expenses, related party			3,900,000
Common Shares of treasury stock distributed (in shares)					33,000
Treasury stock distributed among the persons					14
Percentage of ownership (in hundredths)			100.00%			100.00%
Former Director [Member]
Related Party Transaction [Line Items]
Accounts payable	0	0
Costs and expenses, related party	100,000	100,000	100,000
Immediate Family Member of the Chairman [Member]
Related Party Transaction [Line Items]
Accounts payable	0
Costs and expenses, related party	100,000
Orion Tankers Pool [Member]
Related Party Transaction [Line Items]
Number of tankers withdrawn from pool						9
Nordic American Offshore Limited [Member]
Related Party Transaction [Line Items]
Dividend income recognized	200,000
Company acquired shares in market (In shares)	488,216
Percentage of ownership (in hundredths)	19.20%
Warrants vested (in shares)	333,333
Nordic American Offshore Limited [Member] \| Private Placement [Member]
Related Party Transaction [Line Items]
Private equity placement issued amount		250,000,000
Investment in Nordic American Offshore Ltd		$ 65,000,000
Private equity placement participation (in hundredths)	17.00%	26.00%