Area of a real estate property sold.

No definition available.

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Namespace Prefix:	nen_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the capacity of real estate property.

+ References

No definition available.

+ Details

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Namespace Prefix:	nen_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of real estate properties classified as held for sale as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	nen_NumberOfRealEstatePropertiesHeldForSale
Namespace Prefix:	nen_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of real estate properties sold as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	nen_NumberOfRealEstatePropertiesSold
Namespace Prefix:	nen_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481687/323-10-50-3

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

+ Details

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

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-12

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=nen_CommercialPropertiesInBelmontMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstatePropertiesAxis=us-gaap_WhollyOwnedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=nen_ResidentialAndMixedUseRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=nen_MillStreetGardensResidentialApartmentsWoburnMassachusettsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=nen_ResidentialRetailAndOfficeBuildingMixedUseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=nen_CondominiumRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstatePropertiesAxis=us-gaap_PartiallyOwnedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=nen_CarParkingLotRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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SIGNIFICANT ACCOUNTING POLICIES - Business (Details)	Jan. 28, 2026 USD ($) ft² building	Feb. 01, 2026 ft² item	Dec. 31, 2025 ft² property item	Dec. 31, 2024	Dec. 31, 2023
Commercial Office Buildings
Line of Business
Number of properties			2
Commercial Office Buildings \| Commercial property \| Subsequent Event
Line of Business
Number of real estate properties sold \| building	2
Area of real estate property sold (in square feet) \| ft²	14,000
Properties sold \| $	$ 2,600,000
Loss on sale of properties \| $	$ (400,000)
Commercial Office Buildings \| Belmont Massachusetts property
Line of Business
Number of real estate properties held for sale			2
Partnership properties
Line of Business
Number of properties \| property			34
Partnership properties \| Subsequent Event
Line of Business
Area of property (in square feet) \| ft²		141,000
Partnership properties \| Residential and mixed-use properties
Line of Business
Number of properties \| property			28
Number of units			3,339
Partnership properties \| Apartments
Line of Business
Number of properties \| property			22
Partnership properties \| Apartments \| Mill Street Gardens, LLC Residential Apartments Woburn, Massachusetts \| Subsequent Event
Line of Business
Number of properties		72
Number of units		3,411
Partnership properties \| Mixed use residential, retail and office buildings
Line of Business
Number of properties \| property			6
Partnership properties \| Commercial
Line of Business
Number of properties \| property			6
Area of property (in square feet) \| ft²			145,000
Partnership properties \| Condominium
Line of Business
Number of properties \| property			1
Number of units			19
Investment properties \| Residential and mixed-use properties
Line of Business
Number of units			688
Area of property (in square feet) \| ft²			12,500
Investment properties \| Car parking lot
Line of Business
Capacity of real estate property (in cars per lot)			50
Limited Partnerships \| Investment properties \| Residential and mixed-use properties
Line of Business
Number of properties			7
NERA 40%
Line of Business
Ownership interest (as a percent)			40.00%	40.00%	40.00%
NERA 50%
Line of Business
Ownership interest (as a percent)			50.00%	50.00%	50.00%