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Note J - Treasury Stock (Details Textual) (USD $)
6 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Jun. 02, 2011
Feb. 06, 2015
Equity [Abstract]        
Stock Repurchase Program, Authorized Amount     $ 2,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1  
Treasury Stock, Shares, Acquired 78,864us-gaap_TreasuryStockSharesAcquired 5,100us-gaap_TreasuryStockSharesAcquired    
Treasury Stock Acquired, Average Cost Per Share $ 5.59us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 4.55us-gaap_TreasuryStockAcquiredAverageCostPerShare    
Treasury Stock, Value, Acquired, Cost Method 441,000us-gaap_TreasuryStockValueAcquiredCostMethod 23,000us-gaap_TreasuryStockValueAcquiredCostMethod    
Subsequent Event [Member]        
Equity [Abstract]        
Stock Repurchase Program, Authorized Amount       3,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Stock Repurchase Program, Amount of Additional Shares Authorized to be Repurchased       $ 1,000,000naii_StockRepurchaseProgramAmountOfAdditionalSharesAuthorizedToBeRepurchased
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember