v3.20.2

DERIVATIVES AND FAIR VALUE MEASUREMENTS Narrative 1 (Details) - USD ($) $ in Millions | 1 Months Ended | 5 Months Ended
--- | --- | ---
Jun. 30, 2020 | May 31, 2020
Derivative Instruments, Gain (Loss) [Line Items] |  |
Cash paid from termination of interest rate swaps | $ 49.2 |
Interest rate swaps | Cash Flow Hedges |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Interest rate swaps, interest rate paid |  | 2.80%
Interest rate swaps, interest rate received |  | received a rate based on the three-month USD LIBOR.
Notional amount of forward-starting interest rate swaps terminated |  | $ 250.0

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- Definition Aggregate notional amount that was terminated, specified by the derivative(s). + References No definition available. + Details
Name: | ns_DerivativeNotionalAmountTerminated
Namespace Prefix: | ns_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Interest rate received under the terms of the interest rate swap agreements. + References No definition available. + Details
Name: | ns_InterestRateSwapsInterestRateReceived
Namespace Prefix: | ns_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The premium (cost) of a hedge, net of any cash received on settlement during the period. + References No definition available. + Details
Name: | us-gaap_DerivativeCostOfHedgeNetOfCashReceived
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Fixed interest rate related to the interest rate derivative. + References No definition available. + Details
Name: | us-gaap_DerivativeFixedInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- 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

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- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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