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PARTNERS' EQUITY Table 3 - Cash Distributions Declared - Common Limited Partners (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Distribution Made to Limited Partner [Line Items]              
Common limited partners' distribution, per unit $ 0.40 $ 0.40 $ 0.40 $ 0.40 $ 1.60 $ 2.40 $ 2.40
Common limited partners' distribution $ 43,787 $ 43,678 $ 43,678 $ 43,730 $ 174,873 $ 259,136 $ 248,705
Common Limited Partner [Member]              
Distribution Made to Limited Partner [Line Items]              
Distribution date of record (distribution earned) Feb. 08, 2021 Nov. 06, 2020 Aug. 07, 2020 May 11, 2020      
Distribution payment date Feb. 12, 2021 Nov. 13, 2020 Aug. 13, 2020 May 15, 2020