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Commitments and Contingencies - Schedule of Unrecognized Purchase Commitments (Details) - USD ($) $ in Thousands	4 Months Ended	5 Months Ended	12 Months Ended
	Sep. 30, 2023	Jun. 07, 2023	Dec. 31, 2022
Other Commitments [Line Items]
Gross Commitment	$ 144,700
Unrecorded unconditional purchase obligation, recognized in current period	6,452	$ 8,191	$ 4,976
Remaining Commitment	125,081
Joint Development Agreements, Paid In Cash
Other Commitments [Line Items]
Gross Commitment	70,000
Unrecorded unconditional purchase obligation, recognized in current period	2,867	3,121	2,211
Remaining Commitment	61,801
Joint Development Agreements, Paid In Share-Based Payments
Other Commitments [Line Items]
Gross Commitment	70,000
Unrecorded unconditional purchase obligation, recognized in current period	3,585	3,902	2,765
Remaining Commitment	59,748
Cash | Asset Purchase Commitment
Other Commitments [Line Items]
Gross Commitment	4,700
Unrecorded unconditional purchase obligation, recognized in current period	0	$ 1,168	$ 0
Remaining Commitment	$ 3,532

X

- Definition

Unrecorded Unconditional Purchase Obligation, Gross

+ References

No definition available.

+ Details

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Namespace Prefix:	npwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482648/440-10-50-4

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The amount purchased during the period under an unrecorded unconditional purchase obligation (for example, under the take-or-pay or throughput contract).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482648/440-10-50-4

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- Details

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- Details

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- Details

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