Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013
Line of Credit Facility [Line Items]
Unsecured revolving line of credit	$ 50
Available for borrowings under revolving line of credit	$ 50
Ratio of consolidated indebtedness to earnings before interest, taxes, depreciation and amortization, maximum allowed	3.25
Ratio of consolidated earnings before interest, taxes, depreciation and amortization expense, minimum allowed	3.00
Minimum [Member]
Line of Credit Facility [Line Items]
Quarterly commitment fee	0.175%
Maximum [Member]
Line of Credit Facility [Line Items]
Quarterly commitment fee	0.30%
Base Rate Determined In Accordance With Loan Agreement [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Variable interest rate spread	0.00%
Base Rate Determined In Accordance With Loan Agreement [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Variable interest rate spread	0.50%
LIBOR [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Variable interest rate spread	1.125%
LIBOR [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Variable interest rate spread	2.00%
During Event Of Default [Member]
Line of Credit Facility [Line Items]
Variable interest rate spread	2.00%

Loan agreement, quarterly commitment fee paid on unused portion of line of credit, percentage.

No definition available.

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Period Type:	duration

- Definition

Loan agreement, ratio of consolidated earnings before interest, taxes, depreciation and amortization expense, minimum allowed.

+ References

No definition available.

+ Details

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- Definition

Loan agreement, ratio of consolidated indebtedness to earnings before interest, taxes, depreciation and amortization, maximum allowed.

+ References

No definition available.

+ Details

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Namespace Prefix:	nati_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant