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Leases (Details) - USD ($)	9 Months Ended
	Sep. 30, 2023	Oct. 06, 2023	Jun. 08, 2023	Dec. 31, 2022	Jun. 06, 2022
Lessee, Lease, Description [Line Items]
Lessee, operating lease, discount rate					8.00%
Lease right-of-use asset	$ 181,000			$ 784,000
Measurement Building Lease
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract					60 months
Operating lease, liability	3,000
Lease right-of-use asset	3,000
Roney St. Lease | Subsequent Event
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract		62 months
Operating lease, liability		$ 2,168,000
Lease right-of-use asset		$ 2,144,000
Land
Lessee, Lease, Description [Line Items]
Lease right-of-use asset			$ 210,000
Operating lease, annual lease payment	$ 1

X

- Definition

Operating Lease, Annual Lease Payment

+ References

No definition available.

+ Details

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Namespace Prefix:	npwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-3

+ Details

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

X

- Definition

Discount rate used by lessee to determine present value of operating lease payments.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-3

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	instant

X

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-3

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	instant

X

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479041/842-20-45-1

+ Details

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

X

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479041/842-20-45-1

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Period Type:	instant

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- Details

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Period Type:

X

- Details

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- Details

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- Details

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