RELATED PARTY TRANSACTIONS Narrative 1 (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transactions [Abstract]
Holdco Administrative Services Expense	$ 0.2	$ 1.5	$ 1.7

Related party administrative services expense incurred and/or charged by the company.

No definition available.

Name:	nsh_AdministrativeServicesExpense
Namespace Prefix:	nsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration