The number of active stock incentive plans.

No definition available.

Name:	nwpx_NumberOfActiveStockIncentivePlans
Namespace Prefix:	nwpx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of inactive stock incentive plans.

+ References

No definition available.

+ Details

Name:	nwpx_NumberOfInactiveStockIncentivePlans
Namespace Prefix:	nwpx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of the performance awards issued multiplier.

+ References

No definition available.

+ Details

Name:	nwpx_PerformanceAwardsIssuedMultiplier
Namespace Prefix:	nwpx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the target level percentage for performance share awards.

+ References

No definition available.

+ Details

Name:	nwpx_PerformanceShareAwardTargetLevelPercentage
Namespace Prefix:	nwpx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of non-vested equity-based payment instruments at a target level of performance, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	nwpx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumberAtTargetLevelOfPerformance
Namespace Prefix:	nwpx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=nwpx_RestrictedStockUnitsAndPerformanceStockAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 7 - Share-based Compensation (Details Textual) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) shares	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Number Of Active Stock Incentive Plans	1
Number Of Inactive Stock Incentive Plans	1
Performance Shares [Member]
Performance Share Award Target Level, Percentage	100.00%
Performance Awards Issued Multiplier		132.00%	126.00%	159.00%
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number At Target Level Of Performance (in shares) \| shares	170,000
Performance Shares [Member] \| Minimum [Member]
Performance Awards Issued Multiplier	0.00%
Performance Shares [Member] \| Maximum [Member]
Performance Awards Issued Multiplier	200.00%
Restricted Stock Units and Performance Stock Awards [Member]
Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount \| $	$ 4.4
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 8 months 12 days