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Redeemable Non-Controlling Interests in Subsidiary - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Noncontrolling Interest [Abstract]
Non-controlling interest holders	64.50%	66.00%	64.50%	66.00%

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- Definition

Redeemable Noncontrolling Interest, Percentage Of Common Units

+ References

No definition available.

+ Details

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Namespace Prefix:	npwr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

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- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration