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Costs and Estimated Earnings in Excess of Billings on Uncompleted Contracts and Billings in Excess of Costs and Estimated Earnings - Schedule of Costs and Estimated Earnings in Excess of Billings on Uncompleted Contracts and Billings in Excess of Costs and Estimated Earnings (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Contractors [Abstract] |  |
Costs incurred on uncompleted contracts | $ 265,552 nwpx_CostsIncurredOnUncompletedContracts | $ 182,709 nwpx_CostsIncurredOnUncompletedContracts
Estimated earnings | 53,744 nwpx_EstimatedEarningsOnUncompletedContracts | 37,438 nwpx_EstimatedEarningsOnUncompletedContracts
Sum of costs incurred and estimated earnings on uncompleted contracts | 319,296 nwpx_CostsIncurredAndEstimatedEarningsOnUncompletedContracts | 220,147 nwpx_CostsIncurredAndEstimatedEarningsOnUncompletedContracts
Less billings to date | (276,284)nwpx_BillingsToDateOnUncompletedContracts | (173,047)nwpx_BillingsToDateOnUncompletedContracts
Amounts are presented in the Consolidated Balance Sheets as follows: |  |
Costs and estimated earnings in excess of billings on uncompleted contracts | 45,847 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear | 50,468 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear
Billings in excess of costs and estimated earnings on uncompleted contracts | (2,835)us-gaap_BillingsInExcessOfCostCurrent | (3,368)us-gaap_BillingsInExcessOfCostCurrent
Total, net | $ 43,012 nwpx_CostsAndEstimatedEarningsInExcessOfBillingsAndBillingsInExcessOfCostsAndEstimatedEarningsNet | $ 47,100 nwpx_CostsAndEstimatedEarningsInExcessOfBillingsAndBillingsInExcessOfCostsAndEstimatedEarningsNet

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- Definition Net amount of the total amount included in Cost and Estimated Earnings in Excess of Billings and Billings in Excess of Costs and Estimated Earnings. + References No definition available. + Details
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- Definition Costs incurred and estimated earnings on uncompleted contracts. + References No definition available. + Details
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- Definition Liability attributable to (i) billings in excess of costs under the percentage of completion contract accounting method representing the difference between contractually invoiced amounts (billings) and revenue recognized based, for example, on costs incurred to estimated total costs at period end or (ii) contractually invoiced amounts (billings) in excess of costs incurred and accumulated under the completed contract accounting method that are expected to be realized within one year or one operating cycle, whichever is longer, from the reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57788-111642 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57807-111642 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57795-111642 + Details
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- Definition Amount of receivable reflecting the cost incurred on uncompleted contracts in excess of related billings which is expected to be collected 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 605 -SubTopic 35 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57807-111642 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57795-111642 Reference 3: 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(c)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph c(3) -Article 5 + Details
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