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Note J - Economic Dependency - Substantial Net Purchase From Certain Suppliers (Details) - Supplier Concentration Risk [Member] - Raw Material Purchases [Member] - USD ($) $ in Thousands | 12 Months Ended
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Jun. 30, 2019 | Jun. 30, 2018
Raw Material Purchases by Supplier | $ 8,240 |  | $ 15,214
% of Total Raw Material Purchases | 11.00% |  | 21.00%
Supplier 1 [Member] |  |  |
Raw Material Purchases by Supplier | $ 8,240 |  | $ 7,487
% of Total Raw Material Purchases | 11.00% |  | 10.00%
Supplier 2 [Member] |  |  |
Raw Material Purchases by Supplier |  | [1] | $ 7,727
% of Total Raw Material Purchases |  | [1] | 11.00%
[1] | Purchases were less than 10% of the respective period's total raw material purchases.

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- Definition Percentage of raw materials purchased from supplier + References No definition available. + Details
Name: | naii_PercentageOfRawMaterialsPurchasedFromSupplier
Namespace Prefix: | naii_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Raw material purchases by supplier + References No definition available. + Details
Name: | naii_RawMaterialPurchasesBySupplier
Namespace Prefix: | naii_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_SupplierConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=naii_RawMaterialPurchasesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis=naii_Supplier1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionBySupplierAxis=naii_Supplier2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |