XML 49 R38.htm IDEA: XBRL DOCUMENT v3.8.0.1

Note 7 - Commitments and Contingencies (Details Textual) $ in Millions	1 Months Ended
	Jan. 31, 2017 USD ($)	Jul. 31, 2014 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2014 USD ($)
Number Of Potentially Responsible Parties			100
Estimated Cost of EPA Selected Remedy	$ 1,000.0
Estimated Time to Complete Selected EPA Remedy	13 years
Letters of Credit Outstanding, Amount			$ 2.0
Portland Harbor Natural Resources Trustee Council [Member]
Loss Contingency, Accrual, Current				$ 0.4
Loss Contingency Accrual, Payments		$ 0.2
Lower Willamette Group [Member]
Number Of Potentially Responsible Parties			14

X

- Definition

The estimated cost of the remedy selected by EPA.

+ References

No definition available.

+ Details

Name:	nwpx_EstimatedCostOfEPASelectedRemedy
Namespace Prefix:	nwpx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The estimated amount of time to complete the 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 loss contingency liability expected to be resolved within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&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 cash outflow reducing loss contingency liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

+ Details

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

X

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=nwpx_PortlandHarborNaturalreSourcesTrusteeCouncilMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_CounterpartyNameAxis=nwpx_LowerWillametteGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: