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Note 9 - Commitments and Contingencies (Details Textual) $ in Millions | 1 Months Ended |  |
--- | --- | --- | ---
Jan. 31, 2017 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2014 USD ($)
Number Of Potentially Responsible Parties |  | 100 |
Estimated Cost of EPA Selected Remedy | $ 1,000.0 |  |
Estimated Time to Complete Selected EPA Remedy | 13 years |  |
Letters of Credit Outstanding, Amount |  | $ 2.0 |
Portland Harbor Natural Resources Trustee Council [Member] |  |  |
Loss Contingency, Accrual, Current |  |  | $ 0.4
Lower Willamette Group [Member] |  |  |
Number Of Potentially Responsible Parties |  | 14 |

X
- Definition The estimated cost of the remedy selected by EPA. + References No definition available. + Details
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Namespace Prefix: | nwpx_
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Balance Type: | credit
Period Type: | duration

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- Definition The estimated amount of time to complete the selected EPA remedy. + References No definition available. + Details
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X
- Definition Number of potentially responsible parties for Portland Harbor Superfund site. + References No definition available. + Details
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X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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X
- Definition Amount of loss contingency liability expected to be resolved within one year or the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349 + Details
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- Details
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X
- Details
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Period Type: |