XML 28 R32.htm IDEA: XBRL DOCUMENT v2.4.1.9

Derivative Instruments and Hedging Activities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Mar. 31, 2015 Designated As Hedging Instrument [Member] USD ($)	Mar. 31, 2015 Designated As Hedging Instrument [Member] CAD	Dec. 31, 2014 Designated As Hedging Instrument [Member] USD ($)	Dec. 31, 2014 Designated As Hedging Instrument [Member] CAD
Derivatives, Fair Value [Line Items]
Notional amount of derivative contracts			$ 2,500,000invest_DerivativeNotionalAmount / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember	3,100,000invest_DerivativeNotionalAmount / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember	$ 1,300,000invest_DerivativeNotionalAmount / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember	1,500,000invest_DerivativeNotionalAmount / us-gaap_HedgingDesignationAxis = us-gaap_DesignatedAsHedgingInstrumentMember
Maturity period for Canadian forward contracts	12 months
Gains (losses) from derivative contracts not designated as hedging instruments recognized in net sales	(18,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet	60,000us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Unrealized pretax gain on outstanding derivatives accumulated in other comprehensive loss expected to be reclassified to net sales within next 12 months	$ 21,000us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months	$ 26,000us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Maturity period for forward contracts.

+ References

No definition available.

+ Details

Name:	nwpx_MaturityPeriodForForwardContracts
Namespace Prefix:	nwpx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	us-gaap_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The estimated net amount of unrealized gains or losses on foreign currency cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

+ Details

Name:	us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant