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Related Party Transactions - Schedule of Compensation Payable to BHES (Details) $ in Thousands	Sep. 30, 2025 USD ($)
Related Party Transactions [Abstract]
Compensation Cost Incurred To Date	$ 24,390
Remaining Compensation Cost	2,955
Total Compensation Cost	$ 27,345

X

- Definition

Share-Based Payment Arrangement, Nonvested Award, Compensation Cost

+ References

No definition available.

+ Details

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Namespace Prefix:	npwr_
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Balance Type:	debit
Period Type:	instant

X

- Definition

Share-Based Payment Arrangement, Nonvested Award, Cost Incurred To Date, Amount

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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- References

No definition available.

+ Details

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