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SERIES D CUMULATIVE CONVERTIBLE PREFERRED UNITS Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended 6 Months Ended
Jul. 13, 2018
Jun. 29, 2018
Jul. 13, 2018
Sep. 30, 2018
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Class of Stock [Line Items]              
Proceeds from issuance of Series D preferred units         $ 400,000 $ 0  
Series D preferred units outstanding         15,760,441   0
Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Proceeds from issuance of Series D preferred units   $ 400,000          
Series D preferred units outstanding   15,760,441          
Temporary Equity, Stock Issued During Period, Value, New Issues   $ 370,700          
Transaction fee percentage   3.50%          
Transaction fee   $ 20,700          
Unpaid dividend penalty, Per unit dividend increase         $ 0.048    
Unpaid Dividend Penalty, Preferred Stock, Conversion Basis         each holder of the Series D Preferred Units may elect to convert its Series D Preferred Units into common units on a one-for-one basis    
Unpaid Dividend Penalty, Minimum Amount Of Acquisitions or Asset Sales Requiring Consent         $ 50,000    
Convertible preferred units, terms of redemption         The Partnership may redeem all or any portion of the Series D Preferred Units, in an amount not less than $50.0 million for cash at a redemption price equal to, as applicable: (i) $31.73 per Series D Preferred Unit at any time on or after June 29, 2023 but prior to June 29, 2024; (ii) $30.46 per Series D Preferred Unit at any time on or after June 29, 2024 but prior to June 29, 2025; (iii) $29.19 per Series D Preferred Unit at any time on or after June 29, 2025; plus, in each case, the sum of any unpaid distributions on the applicable Series D Preferred Unit plus the distributions prorated for the number of days elapsed (not to exceed 90) in the period of redemption (Series D Partial Period Distributions). The holders have the option to convert the units prior to such redemption as discussed above. Additionally, at any time on or after June 29, 2028, each holder of Series D Preferred Units will have the right to require the Partnership to redeem all of the Series D Preferred Units held by such holder at a redemption price equal to $29.19 per Series D Preferred Unit plus any unpaid Series D distributions plus the Series D Partial Period Distributions. If a holder of Series D Preferred Units exercises its redemption right, the Partnership may elect to pay up to 50% of such amount in common units (which shall be valued at 93% of a volume-weighted average trading price of the common units; provided, that the common units to be issued do not, in the aggregate, exceed 15% of NuStar Energy’s common equity market capitalization at the time.    
Maximum number of days within partial distribution period         90    
Convertible Preferred Stock, Terms of Conversion, Change of Control         convert its Series D Preferred Units into common units on a one-for-one basis, plus any unpaid Series D distributions    
Change of control redemption amount         the sum of (a) $29.82 per Series D Preferred Unit plus (b) any unpaid Series D distributions plus (c) the applicable distribution amount for the distribution periods ending after the change of control event and prior to (but including) the fourth anniversary of the Initial Closing    
Temporary equity, accounting treatment         The Series D Preferred Units are considered redeemable securities under GAAP due to the existence of redemption provisions at the option of the holders of the Series D Preferred Units and upon a Series D Change of Control (as defined in the partnership agreement), which is outside the Partnership’s control. Therefore, they are presented as temporary equity in the mezzanine section of the consolidated balance sheets. The Series D Preferred Units have been recorded at their issuance date fair value, net of issuance costs. We reassess the presentation of the Series D Preferred Units in our consolidated balance sheets on a quarterly basis. The Series D Preferred Units are subject to accretion from their carrying value at the issuance date to the redemption value, which is based on the redemption right of the Series D Preferred Unit holders that may be exercised at any time on or after June 29, 2028, using the effective interest method over a period of ten years. The accretion will be treated in the same manner as a distribution and deducted from net income to arrive at net income attributable to common units.    
Accretion period         10 years    
Subsequent Event [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Proceeds from issuance of Series D preferred units $ 190,000   $ 590,000        
Issuance of preferred units (temporary equity) (in units) 7,486,209   7,486,209        
Units issued, price per unit $ 25.38   $ 25.38        
Series D preferred units outstanding 23,246,650   23,246,650        
Temporary Equity, Stock Issued During Period, Value, New Issues $ 185,200   $ 555,900        
Equity issuance costs     $ 13,400        
Distribution payment date       Sep. 17, 2018      
Distribution date of record       Sep. 04, 2018      
Preferred Stock, Distributions, Period - June 29, 2018 to June 28, 2020 [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Preferred units distribution percentage         9.75%    
Preferred Stock, Distributions, Period - June 29, 2020 to June 28, 2023 [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Preferred units distribution percentage         10.75%    
Preferred Stock, Distributions, Period - June 29, 2023 and thereafter [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Preferred units, dividend payment rate, variable         the greater of 13.75% per annum or the common unit distribution rate thereafter    
Preferred Stock, Distributions, Period - June 29, 2023 and thereafter [Member] | Minimum [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Preferred units distribution percentage         13.75%    
Preferred Stock, Distributions, Period - June 29, 2018 to June 15, 2019 [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Maximim percentage of distributions that may be paid in additional units         50.00%    
Preferred Stock Distributions, Period - June 16, 2019 and thereafter [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Required amount of per unit cash dividends to permit dividend paid in kind         $ 0.635    
Preferred Stock, Issuer Redemption, Period - June 29, 2023 to June 28, 2024 [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Temporary equity redemption price per unit         $31.73 per Series D Preferred Unit plus any unpaid Series D distributions plus the Series D Partial Period Distributions    
Preferred Stock, Issuer Redemption, Period - June 29, 2023 and thereafter [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Minimum redemption amount         $ 50,000    
Preferred Stock, Issuer Redemption, Period - June 29, 2024 to June 28, 2025 [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Temporary equity redemption price per unit         $30.46 per Series D Preferred Unit plus any unpaid Series D distributions plus the Series D Partial Period Distributions    
Preferred Stock, Issuer Redemption, Period - June 29, 2025 and thereafter [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Temporary equity redemption price per unit         $29.19 per Series D Preferred Unit plus any unpaid Series D distributions plus the Series D Partial Period Distributions    
Preferred Stock, Holder Redemption, Period - June 29, 2028 and thereafter [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Temporary equity redemption price per unit         $29.19 per Series D Preferred Unit plus any unpaid Series D distributions plus the Series D Partial Period Distributions    
Percentage of redemption amount that may be paid in common limited partner units         50.00%    
Volume-weighted average trading price percentage of common limited partner units         93.00%    
Common limited partners' equity market capitalization, maximum allowable percentage         15.00%    
Preferred Stock, Conversion, Period - June 29, 2020 and thereafter [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Convertible preferred units, terms of conversion         At any time on or after June 29, 2020, each holder of Series D Preferred Units may convert all or any portion of its Series D Preferred Units into common units on a one-for-one basis (plus any unpaid Series D distributions), subject to anti-dilution adjustments, at any time, but not more than once per quarter, so long as any conversion is for at least $50.0 million based on the Series D Preferred Unit Purchase Price (or such lesser amount representing all of a holder’s Series D Preferred Units).    
Minimum conversion amount         $ 50,000    
Equity Issuance Date, June 29, 2018 [Member] | Subsequent Event [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Preferred unit distribution declared       $ 0.525      
Equity Issuance Date, July 13, 2018 [Member] | Subsequent Event [Member] | Series D Preferred Limited Partner [Member]              
Class of Stock [Line Items]              
Preferred unit distribution declared       $ 0.431