UNIT-BASED COMPENSATION PLANS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
LTIP and Option Plan
Share-based Compensation Arrangement by Share-based Payment Award
Compensation expense	$ 5.9	$ 4.9	$ 21.6	$ 21.7
Long Term Incentive Plan 2009, Deferral Plan | Phantom Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Awards granted (in shares)			529,859
Long Term Incentive Plan 2009, Deferral Plan | Phantom Stock Units | Employee
Share-based Compensation Arrangement by Share-based Payment Award
Awards granted (in shares)			158,970
Long Term Incentive Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award
Awards granted (in shares)			908,000
Long Term Incentive Plan 2013 | Phantom Stock Units | Independent Directors
Share-based Compensation Arrangement by Share-based Payment Award
Awards granted (in shares)			32,247
Long Term Incentive Plan 2013 | Performance Shares | Employee
Share-based Compensation Arrangement by Share-based Payment Award
Awards granted (in shares)			345,943