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SUBSEQUENT EVENTS (Details) |  |  | 3 Months Ended | 12 Months Ended | 115 Months Ended
--- | --- | --- | --- | --- | ---
Mar. 31, 2017 shares | Aug. 20, 2007 shares | Mar. 31, 2017 shares | Dec. 31, 2016 $ / item | Mar. 31, 2017 $ / item
Subsequent events |  |  |  |  |
Repurchase price of depository receipts (in dollars per receipt) | $ / item |  |  |  |  | 27.14
Number of depository receipts repurchased | shares | 1,365,306 | 1,365,306 |  |  |
Quarterly distribution per unit (in dollars per unit) | $ / item |  |  |  | 7.50 |
Quarterly distributions per depositary receipt (in dollars per receipt) | $ / item |  |  |  | 0.25 |
Special distribution per unit (in dollars per unit) | $ / item |  |  |  | 24.00 |
Special distribution per depository receipt (in dollars per receipt) | $ / item |  |  |  | 0.80 |
General Partnership |  |  |  |  |
Subsequent events |  |  |  |  |
Repurchases required (in units) | shares |  |  | 0.2 |  |
Number of depository receipts repurchased | shares | 162 | 162 |  |  |
Class B |  |  |  |  |
Subsequent events |  |  |  |  |
Repurchases required (in units) | shares |  |  | 4.3 |  |
Number of depository receipts repurchased | shares | 3,072 | 3,072 |  |  |

X
- Definition Represents the number of depository receipts repurchased under the equity repurchase program. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the average price at which depository receipts are repurchased under the equity repurchase program. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the quarterly distributions per depository receipt. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the amount of quarterly distribution per unit of limited partner interest. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the special distribution per depository receipt. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the amount of special distribution per unit of limited partner interest. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the repurchase of units required. + References No definition available. + Details
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Namespace Prefix: | nen_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |