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Note K - Share-based Compensation (Details Textual) (USD $)
3 Months Ended 9 Months Ended
Dec. 28, 2014
Dec. 29, 2013
Dec. 28, 2014
Dec. 29, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition     1 year 120 days  
Stock options $ 228,000us-gaap_AllocatedShareBasedCompensationExpense $ 192,000us-gaap_AllocatedShareBasedCompensationExpense $ 629,000us-gaap_AllocatedShareBasedCompensationExpense $ 530,000us-gaap_AllocatedShareBasedCompensationExpense
Share Based Compensation Total Unamortized Compensation Expense 2,044,000nath_ShareBasedCompensationTotalUnamortizedCompensationExpense   2,044,000nath_ShareBasedCompensationTotalUnamortizedCompensationExpense  
Granted (in shares)     50,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross  
Granted (in dollars per share)     $ 53.89us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice  
Share Based Compensation Arrangement by Share Based Payment Award Option Life     5 years  
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period     4 years  
Restricted Stock [Member]        
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition       5 years
Stock options 135,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
136,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
405,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
362,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period       5 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period       25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value       $ 49.80us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized   $ 1,245,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
  $ 1,245,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember