DISPOSITIONS, ACQUISITIONS AND DROP DOWN TRANSACTIONS - 2016 Drop Down (Details) - Drop Down Assets 2016 Acquisition - USD ($) $ in Millions			1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Mar. 03, 2016	Jun. 30, 2016	Mar. 31, 2019	Sep. 30, 2019	Jun. 30, 2020	Feb. 26, 2019
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 360.0
Working capital adjustment			$ 0.6
Remaining cash consideration payable						$ 303.5	$ 303.5
Remaining consideration description				Remaining Consideration at $303.5 million, with such amount to be paid by the Partnership in one or more payments over the period from March 1, 2020 through December 31, 2020, in (i) cash, (ii) the Partnership’s common units or (iii) a combination of cash and the Partnership’s common units, at the discretion of the Partnership. At least 50% of the Remaining Consideration must be paid on or before June 30, 2020 and interest will accrue at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020	the remaining portion of the consideration due to SMP Holdings will be $180.75 million (the “Remaining Consideration”). The parties have also agreed to extend the final date by which the Partnership is obligated to deliver the Remaining Consideration to January 15, 2022. The Remaining Consideration remains payable to SMP Holdings in (i) cash, (ii) the Partnership’s common units or (iii) a combination of cash and the Partnership’s common units, and interest continues to accrue (and is payable quarterly in cash) at a rate of 8% per annum on any portion of the Remaining Consideration that remains unpaid after March 31, 2020.
Estimated future payment obligation					$ 295.8
Deferred purchase price obligation					$ 303.5
Discount rate					5.25%
Scenario Forecast
Business Acquisition [Line Items]
Annual accrued Interest rate on unpaid consideration	8.00%
Scenario Forecast | Minimum
Business Acquisition [Line Items]
Minimum remaining consideration to be paid percentage						50.00%