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Note 18 - Accumulated Other Comprehensive Loss - Summary of Accumulated Other Comprehensive Loss (Details) (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Foreign Exchange Forward [Member]
Accumulated Other Comprehensive Income (Loss) Cumulative Change in Net Gain (Loss) from Cash Flow Hedge Effect, Tax	$ (9)	$ 12
Interest Rate Swap [Member]
Accumulated Other Comprehensive Income (Loss) Cumulative Change in Net Gain (Loss) from Cash Flow Hedge Effect, Tax	24	79
Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) Defined Benefit Pension and Other Postretirement Plans Tax Expense (Benefit)	$ 392	$ 482

X

- Definition

Tax expense (benefit) included in accumulated other comprehensive income for cash flow hedges.

+ References

No definition available.

+ Details

Name:	nwpx_AccumulatedOtherComprehensiveIncomeLossCumulativeChangeInNetGainLossFromCashFlowHedgeEffectTax
Namespace Prefix:	nwpx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Tax expense (benefit) included in accumulated other comprehensive income for defined benefit pension and other postretirement plans.

+ References

No definition available.

+ Details

Name:	nwpx_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansTaxExpenseBenefit
Namespace Prefix:	nwpx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: