PARTNERS' CAPITAL AND DISTRIBUTIONS - Narrative (Details)	1 Months Ended		9 Months Ended
	Nov. 30, 2018 shares	Mar. 30, 2018 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)
Partner's capital and distributions
Net proceeds from issuance of Units and exercise of Unit options			$ 0	$ 261,958,000
Class C Units
Partner's capital and distributions
Units issued in private placements | shares		6,200,000
Aggregate proceeds of private placement		$ 265,000,000.0
Net proceeds from issuance of Units and exercise of Unit options		$ 262,000,000.0
Issuance costs					$ 3,000,000.0
Shares converted (in shares) | shares	6,714,963
Conversion basis	1
Prior Credit Facility | Line of Credit
Partner's capital and distributions
Maximum borrowing capacity			$ 1,500,000,000