INCOME TAXES Narrative 2 - Capital Loss Carryforwards (Details) - U.S. [Member] $ in Millions	Dec. 31, 2020 USD ($)
Capital Loss Carryforwards [Line Items]
Capital loss carryforward	$ 51.5
Capital loss carryforward, subject to limitations	$ 17.7

Amount of capital loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

No definition available.

Name:	ns_CapitalLossCarryforwards
Namespace Prefix:	ns_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant