XML 19 R42.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Share-based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified | 6 Months Ended
--- | ---
Jun. 30, 2014 | Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of inactive stock option plan | 1 |
Number of active stock incentive plan | 1 |
RSUs and PSAs at target level of performance included in unvested balance | 188,000 |
Minimum performance awards issued multiplier | 0.00% |
Maximum performance awards issued multiplier | 200.00% |
Directors [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock awards granted to non-employee directors | 7,640 | 4,912
Grant date fair market value of stock awards | $ 36.00 | $ 27.49
Minimum [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period of market-based PSAs | 2 years |
Maximum [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period of market-based PSAs | 3 years |
Restricted Stock Units and Performance Stock Awards [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Unrecognized compensation expense | $ 5.9 |
Expected weighted average period of compensation expense to be recognized | 2 years 1 month 6 days |

X
- Definition Maximum performance awards issued multiplier. + References No definition available. + Details
Name: | nwpx_MaximumPerformanceAwardsIssuedMultiplier
Namespace Prefix: | nwpx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Minimum performance awards issued multiplier. + References No definition available. + Details
Name: | nwpx_MinimumPerformanceAwardsIssuedMultiplier
Namespace Prefix: | nwpx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of active stock incentive plans. + References No definition available. + Details
Name: | nwpx_NumberOfActiveStockIncentivePlans
Namespace Prefix: | nwpx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of inactive stock option plans. + References No definition available. + Details
Name: | nwpx_NumberOfInactiveStockOptionPlans
Namespace Prefix: | nwpx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of non-vested equity-based payment instruments at a target level of performance, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References No definition available. + Details
Name: | nwpx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumberAtTargetLevelOfPerformance
Namespace Prefix: | nwpx_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Share Based Compensation Arrangement By Share Based Payment Award Performance Stock Award Vesting Period + References No definition available. + Details
Name: | nwpx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceStockAwardVestingPeriod
Namespace Prefix: | nwpx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based compensation arrangement by stock based payment award grant date fair value. + References No definition available. + Details
Name: | nwpx_ShareBasedCompensationArrangementByStockBasedPaymentAwardGrantDateFairValue
Namespace Prefix: | nwpx_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
Name: | us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation. + References No definition available. + Details
Name: | us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition The number of shares or units of entity securities issued in the transaction in which equity securities were issued to pay for goods or nonemployee services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6406099&loc=d3e25284-112666 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedGoodsAndNonemployeeServicesTransactionQuantityOfSecuritiesIssued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration