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Note 12 - Shareholder Rights Plan (Details Textual) - $ / shares	Jun. 18, 2009	Dec. 31, 2015
Amended and Restated Rights Agreement Expiration Date	Jun. 28, 2019
Number of Series Junior Participating Preferred Stock Shares Reserved		150,000
Dividend Distribution Under Shareholder Rights Plan		1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right		0.01
Purchase Price Under Rights		$ 83
Acquisition Percentage		15.00%
Value of Exercised Right		2
Right Redemption Value		$ 0.01

X

- Definition

Percentage of Company's outstanding shares of common stock which person or group must acquire or commence a tender offer to acquire to cause Rights to become exercisable.

+ References

No definition available.

+ Details

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X

- Definition

Represents the amended and restated rights agreement expiration date

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Namespace Prefix:	nwpx_
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X

- Definition

Dividend distribution under shareholder rights plan.

+ References

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+ Details

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X

- Definition

Number of Series A Junior Participating Preferred Stock Shares reserved under the Shareholder Rights Plan.

+ References

No definition available.

+ Details

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X

- Definition

Price at which shareholders holding a Right may purchase 1/100th of a share of preferred stock under the Shareholder Rights Plan.

+ References

No definition available.

+ Details

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Balance Type:	na
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X

- Definition

Under certain circumstances, the value at which the Company may redeem the right.

+ References

No definition available.

+ Details

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Data Type:	num:perShareItemType
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X

- Definition

If exercised, the value of common stock of the Company or an acquiring company a Right holder may purchase. This amount is equal to two times the exercise price of the Right.

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X

- Definition

Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares.

+ References

No definition available.

+ Details

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