XML 55 R53.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Long Term Debt (Details Textual) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Long Term Debt (Textual) [Abstract] |  |  |
Interest expense under credit agreement and long-term debt | $ 5,600,000 | $ 9,300,000 | $ 8,900,000
Capitalized interest on long-term debt | 200,000 | 200,000 | 500,000
Series A Term Note [Member] |  |  |
Annual term note payment | 2,100,000 |  |
Quarterly paid interest rate | 10.50% |  |
Series B Term Note [Member] |  |  |
Annual term note payment | 1,500,000 |  |
Quarterly paid interest rate | 10.22% |  |
Series C Term Note [Member] |  |  |
Annual term note payment | 1,400,000 |  |
Quarterly paid interest rate | 9.11% |  |
Series D Term Note [Member] |  |  |
Annual term note payment | $ 643,000 |  |
Quarterly paid interest rate | 9.07% |  |

X
- Definition Interest on long-term debt capitalized during the fiscal year. + References No definition available. + Details
Name: | nwpx_InterestOnLongTermDebtCapitalized
Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Long term debt annual repayment due amount. + References No definition available. + Details
Name: | nwpx_LongTermDebtAnnualRepaymentDueAmount
Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | nwpx_LongTermDebtTextualAbstract
Namespace Prefix: | nwpx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The average effective interest rate during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 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 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateDuringPeriod
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.8) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 8 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 34 -Paragraph 21 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_InterestExpenseDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration