XML 86 R60.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Leases - Additional information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Leases [Abstract] |  |  |
Capital lease obligations outstanding | $ 7.9 |  |
Weighted average interest rate on capital leases | 7.04% |  |
Capital leases outstanding under Bossier City Financing Arrangement | 5.4 |  |
Rental expenses | $ 3.1 | $ 3.2 | $ 3.3
Maximum duration of operating leases (in years) | 10 years |  |

X
- Definition Capital lease obligation under financial arrangement. + References No definition available. + Details
Name: | nwpx_CapitalLeaseObligationUnderFinancialArrangement
Namespace Prefix: | nwpx_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition The weighted average interest rate on capital leases. + References No definition available. + Details
Name: | nwpx_CapitalLeaseWeightedAverageInterestRate
Namespace Prefix: | nwpx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Maximum duration of operating leases (in years). + References No definition available. + Details
Name: | nwpx_MaximumDurationOfOperatingLeases
Namespace Prefix: | nwpx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737 + Details
Name: | us-gaap_CapitalLeaseObligations
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717 + Details
Name: | us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration