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Note I - Treasury Stock (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 28, 2017	May 11, 2015	Feb. 06, 2015	Jun. 02, 2011
Stock Repurchase Program, Authorized Amount					$ 7,000,000	$ 5,000,000	$ 3,000,000	$ 2,000,000
Shares Paid for Tax Withholding for Share Based Compensation	7,264	367	7,998	6,404
Shares Paid for Tax Withholding for Share-based Compensation, Average Cost Per Share	$ 10.80	$ 12.30	$ 10.79	$ 13.09
Payments Related to Tax Withholding for Share-based Compensation	$ 78,000	$ 5,000	$ 86,000	$ 84,000
Excluding Restricted Stock Purchased [Member]
Treasury Stock, Shares, Acquired	0	0	0	0
2015 Increase [Member]
Stock Repurchase Program, Authorized Amount						$ 2,000,000	$ 1,000,000
2017 Increase [Member]
Stock Repurchase Program, Authorized Amount					$ 2,000,000

X

- Definition

Represents the total cost of shares paid for tax withholding for share-based compensation divided by the total number of shares paid for tax withholding for share-based compensation.

+ References

No definition available.

+ Details

Name:	naii_SharesPaidForTaxWithholdingForShareBasedCompensationAverageCostPerShare
Namespace Prefix:	naii_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 25
-Paragraph 19A
-URI http://asc.fasb.org/extlink&oid=96949009&loc=SL79513924-113897

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Namespace Prefix:	us-gaap_
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X

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

X

- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

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- Details

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X

- Details

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X

- Details

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