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TREASURY UNITS (Details) (USD $)
0 Months Ended 12 Months Ended 76 Months Ended 88 Months Ended 2 Months Ended
Aug. 08, 2008
Aug. 20, 2007
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2014
Mar. 10, 2015
Mar. 06, 2008
Jan. 30, 2008
Jan. 15, 2008
Jan. 03, 2012
Treasury units     52,572nen_PartnersCapitalAccountTreasuryUnitsIssued       52,572nen_PartnersCapitalAccountTreasuryUnitsIssued 52,572nen_PartnersCapitalAccountTreasuryUnitsIssued          
Period for repurchase of depository receipts 12 months 12 months                      
Depository receipts authorized to be repurchased   300,000nen_PartnersCapitalAccountDepositoryReceiptsTreasuryReceiptsAuthorizedToBeRepurchased             2,000,000nen_PartnersCapitalAccountDepositoryReceiptsTreasuryReceiptsAuthorizedToBeRepurchased 1,500,000nen_PartnersCapitalAccountDepositoryReceiptsTreasuryReceiptsAuthorizedToBeRepurchased 900,000nen_PartnersCapitalAccountDepositoryReceiptsTreasuryReceiptsAuthorizedToBeRepurchased 600,000nen_PartnersCapitalAccountDepositoryReceiptsTreasuryReceiptsAuthorizedToBeRepurchased  
Repurchase of depository receipts     44,025nen_PartnersCapitalAccountDepositoryReceiptsTreasury 22,964nen_PartnersCapitalAccountDepositoryReceiptsTreasury   1,286,916nen_PartnersCapitalAccountDepositoryReceiptsTreasury   1,286,916nen_PartnersCapitalAccountDepositoryReceiptsTreasury          
Repurchase price of depository receipts     $ 47.90nen_PartnersCapitalAccountDepositoryReceiptsTreasuryAverageRepurchasePricePerDepositoryReceipt $ 37.80nen_PartnersCapitalAccountDepositoryReceiptsTreasuryAverageRepurchasePricePerDepositoryReceipt     $ 25.65nen_PartnersCapitalAccountDepositoryReceiptsTreasuryAverageRepurchasePricePerDepositoryReceipt            
Repurchase price of units     $ 1,437nen_PartnersCapitalAccountUnitsTreasuryAverageRepurchasePricePerUnit $ 1,134nen_PartnersCapitalAccountUnitsTreasuryAverageRepurchasePricePerUnit                  
Repurchase of units     1,834us-gaap_PartnersCapitalAccountUnitsTreasury 957us-gaap_PartnersCapitalAccountUnitsTreasury 1,040us-gaap_PartnersCapitalAccountUnitsTreasury                
Total cost of repurchase     $ 2,685,583us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases $ 1,094,609us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases $ 906,214us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases   $ 35,167,000us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases            
Subsequent event                          
Repurchase of depository receipts                 19,415nen_PartnersCapitalAccountDepositoryReceiptsTreasury
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
Repurchase price of depository receipts                 $ 50.00nen_PartnersCapitalAccountDepositoryReceiptsTreasuryAverageRepurchasePricePerDepositoryReceipt
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
Repurchase price of units                 $ 1,500.00nen_PartnersCapitalAccountUnitsTreasuryAverageRepurchasePricePerUnit
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
Repurchase of depository receipts                 975,731nen_PartnersCapitalAccountDepositoryReceiptsTreasuryRepurchased
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
Class A                          
Treasury units     42,057nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
      42,057nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
42,057nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
         
Number of units in each depository receipt   0.1dei_EntityListingDepositoryReceiptRatio
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
                    0.03333dei_EntityListingDepositoryReceiptRatio
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
Fixed distribution percentage of unit holders     80.00%nen_PartnersCapitalAccountFixedDistributionPercentageOfHoldersOfUnits
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
                   
Repurchase price of units             $ 769.50nen_PartnersCapitalAccountUnitsTreasuryAverageRepurchasePricePerUnit
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
           
Total cost of repurchase     2,158,332us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
877,623us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
726,058us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassAMember
               
Class B                          
Treasury units     9,989nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
      9,989nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
9,989nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
         
Fixed distribution percentage of unit holders     19.00%nen_PartnersCapitalAccountFixedDistributionPercentageOfHoldersOfUnits
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
                   
Repurchase of depository receipts             2,452nen_PartnersCapitalAccountDepositoryReceiptsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
           
Repurchase price of units             $ 769.53nen_PartnersCapitalAccountUnitsTreasuryAverageRepurchasePricePerUnit
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
           
Repurchase of units     349us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
182us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
    2,452us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
           
Total cost of repurchase     500,888us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
206,137us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
171,148us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
               
Class B | Subsequent event                          
Repurchase of units                 154us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
Total cost of repurchase                 230,574us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= nen_LimitedClassBMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
General Partnership                          
Treasury units     526nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
      526nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
526nen_PartnersCapitalAccountTreasuryUnitsIssued
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
         
Fixed distribution percentage of unit holders     1.00%nen_PartnersCapitalAccountFixedDistributionPercentageOfHoldersOfUnits
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
                   
Repurchase price of units             $ 769.53nen_PartnersCapitalAccountUnitsTreasuryAverageRepurchasePricePerUnit
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
           
Repurchase of units     18us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
10us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
  129us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
129us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
           
Total cost of repurchase     26,363us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
10,849us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
9,008us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
               
General Partnership | Subsequent event                          
Repurchase of units                 8us-gaap_PartnersCapitalAccountUnitsTreasury
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
       
Total cost of repurchase                 $ 12,135us-gaap_PartnersCapitalAccountTreasuryUnitsPurchases
/ us-gaap_PartnerTypeOfPartnersCapitalAccountAxis
= us-gaap_GeneralPartnerMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember