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Note 7 - Schedule of Future Minimum Lease Payments for Capital Leases (Details) (Parentheticals)	Dec. 31, 2015
Capita Llease Weighted Average Interest Rate	4.87%

X

- Definition

Represents 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