XML 33 R71.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Commitments and Contingencies - Additional Information (Detail) (USD $) | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2007 | Jan. 31, 2015 | Jul. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2013 | Jun. 30, 2014
Other Commitments [Line Items] |  |  |  |  |  |
Company made payment to Lower Willamette Group as interim settlement | $ 200,000 us-gaap_LitigationSettlementAmount |  |  |  |  |
Amount spent for Source Control work |  |  |  | 100,000 nwpx_AmountSpentToCompleteWorkSpecifiedInWorkPlans |  |
Amount spent for further Source Control work |  |  |  | 100,000 nwpx_AmountSpentForFurtherSourceControlWork |  |
Number of potentially responsible parties |  |  |  | 100 nwpx_NumberOfPotentiallyResponsibleParties |  |
Trades and other receivables |  |  |  | 58,310,000 us-gaap_ReceivablesNetCurrent | 72,470,000 us-gaap_ReceivablesNetCurrent |
Total stand-by letters of credit |  |  |  | 2,300,000 us-gaap_LettersOfCreditOutstandingAmount |  |
Subsequent Event [Member] |  |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |  |
Company made payment to Lower Willamette Group as interim settlement |  | 2,600,000 us-gaap_LitigationSettlementAmount / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |
Settled Litigation [Member] |  |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |  |
Trades and other receivables |  |  |  | 2,600,000 us-gaap_ReceivablesNetCurrent / us-gaap_LitigationStatusAxis = us-gaap_SettledLitigationMember |  |
Portland Harbor Natural Resources Trustee Council [Member] |  |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |  |
Injury assessment process, payment |  |  | 200,000 us-gaap_LossContingencyAccrualCarryingValuePayments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = nwpx_PortlandHarborNaturalResourcesTrusteeCouncilMember |  |  |
Injury assessment process, outstanding |  |  |  |  |  | 400,000 us-gaap_LossContingencyAccrualCarryingValueCurrent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = nwpx_PortlandHarborNaturalResourcesTrusteeCouncilMember
Minimum [Member] |  |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |  |
Estimated cost |  |  |  | 169,000,000 nwpx_EstimatedCostOfEpaSelectedRemedy / us-gaap_RangeAxis = us-gaap_MinimumMember |  |
Estimated years to implement |  |  |  | 2 years |  |
Maximum [Member] |  |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |  |
Estimated cost |  |  |  | $ 1,760,000,000 nwpx_EstimatedCostOfEpaSelectedRemedy / us-gaap_RangeAxis = us-gaap_MaximumMember |  |
Estimated years to implement |  |  |  | 28 years |  |

X
- Definition Amount Spent For Further Source Control Work + References No definition available. + Details
Name: | nwpx_AmountSpentForFurtherSourceControlWork
Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount spent to complete work specified in work plans. + References No definition available. + Details
Name: | nwpx_AmountSpentToCompleteWorkSpecifiedInWorkPlans
Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Estimated cost of EPA selected remedy. + References No definition available. + Details
Name: | nwpx_EstimatedCostOfEpaSelectedRemedy
Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated time to complete selected EPA remedy. + References No definition available. + Details
Name: | nwpx_EstimatedTimeToCompleteSelectedEpaRemedy
Namespace Prefix: | nwpx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of potentially responsible parties for Portland Harbor Superfund site. + References No definition available. + Details
Name: | nwpx_NumberOfPotentiallyResponsibleParties
Namespace Prefix: | nwpx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of judgment or settlement awarded to (against) the entity in respect of litigation. + References No definition available. + Details
Name: | us-gaap_LitigationSettlementAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 + Details
Name: | us-gaap_LossContingencyAccrualCarryingValueCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of payments made reducing loss contingency liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 + Details
Name: | us-gaap_LossContingencyAccrualCarryingValuePayments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_OtherCommitmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph a -Article 5 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 210.5-02.3,4) -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 4 -Article 5 + Details
Name: | us-gaap_ReceivablesNetCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_LitigationStatusAxis=us-gaap_SettledLitigationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=nwpx_PortlandHarborNaturalResourcesTrusteeCouncilMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |