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Note P - Subsequent Event (Details Textual) (USD $)
12 Months Ended 162 Months Ended 0 Months Ended
Mar. 29, 2015
Mar. 29, 2015
Jun. 10, 2015
Aug. 07, 2015
Mar. 27, 2015
Sep. 11, 2014
Mar. 30, 2014
Dec. 13, 2013
Feb. 13, 2013
Treasury Stock, Shares, Acquired 37,661us-gaap_TreasuryStockSharesAcquired 4,647,687us-gaap_TreasuryStockSharesAcquired              
Common Stock, Par or Stated Value Per Share $ 0.01us-gaap_CommonStockParOrStatedValuePerShare $ 0.01us-gaap_CommonStockParOrStatedValuePerShare       $ 0.01us-gaap_CommonStockParOrStatedValuePerShare $ 0.01us-gaap_CommonStockParOrStatedValuePerShare $ 0.01us-gaap_CommonStockParOrStatedValuePerShare $ 0.01us-gaap_CommonStockParOrStatedValuePerShare
Share Price         $ 73.56us-gaap_SharePrice       $ 36.87us-gaap_SharePrice
Chief Operating Officer [Member] | Subsequent Event [Member]                  
Consulting Agreement Term     1 year            
Treasury Stock, Shares, Acquired     56,933us-gaap_TreasuryStockSharesAcquired
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefOperatingOfficerMember
           
Chief Operating Officer [Member] | Scenario, Forecast [Member]                  
Consulting Fee Per Month       $ 16,291nath_ConsultingFeePerMonth
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefOperatingOfficerMember
         
Severance Costs       $ 288,750us-gaap_SeveranceCosts1
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefOperatingOfficerMember
         
Subsequent Event [Member]                  
Common Stock, Par or Stated Value Per Share     0.01us-gaap_CommonStockParOrStatedValuePerShare
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
           
Share Price     40.28us-gaap_SharePrice
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember