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Note 18 - Accumulated Other Comprehensive Loss - Summary of Accumulated Other Comprehensive Loss (Details) (Parentheticals) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021
Foreign Exchange Forward [Member] |  |
Unrealized gain (loss) on cash flow hedges, tax effect | $ (33) | $ 61
Interest Rate Swap [Member] |  |
Unrealized gain (loss) on cash flow hedges, tax effect | (213) | 0
Pension Plan [Member] |  |
Pension liability adjustment, tax effect | $ 592 | $ 577

X
- Definition Tax expense (benefit) included in accumulated other comprehensive income for cash flow hedges. + References No definition available. + Details
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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
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Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
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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
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |