EQUITY COMPENSATION (Restricted Units) (Details) - USD ($) $ / shares in Units, $ in Millions						1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 17, 2019	Sep. 16, 2019	Jun. 14, 2019	Mar. 15, 2019	Jul. 31, 2018	Jul. 31, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity compensation
Dividend declared and paid per share of Class A common stock (in dollar per share)	$ 0.32	$ 0.32	$ 0.32	$ 0.32			$ 0.32	$ 0.32	$ 0.32	$ 0.32	$ 0.28	$ 0.28	$ 0.28	$ 0.24	$ 1.28	$ 1.33	$ 1.13
Distribution equivalents made to holders															$ 21.5
Weighted Average Grant Date Fair Value
Unrecognized compensation expenses							$ 90.5								$ 90.5
Restricted units
Equity compensation
Granted (in units)						2,000,000									4,499,563
Units
Balance at the beginning of the period (in units or shares)										16,255,475					16,255,475
Granted (in units)						2,000,000									4,499,563
Vested (in units)															(3,691,234)
Forfeited (in units)															(253,331)
Balance at the end of the period (in units or shares)							16,810,473				16,255,475				16,810,473	16,255,475
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)										$ 19.21					$ 19.21
Granted (in dollars per share)															21.42
Vested (in dollars per share)															17.96
Forfeited (in dollars per share)															19.68
Balance at the end of the period (in dollars per share)							$ 20.07				$ 19.21				$ 20.07	$ 19.21
Unrecognized compensation expenses							$ 203.0								$ 203.0
Weighted average period of compensation expense expected to be recognized															2 years 9 months 21 days
Contingent Vesting Units Awards
Equity compensation
Granted (in units)						1,333,334
Units
Granted (in units)						1,333,334
Restricted units with a market condition
Equity compensation
Granted (in units)						666,666									0
Units
Balance at the beginning of the period (in units or shares)										1,333,334					1,333,334
Granted (in units)						666,666									0
Vested (in units)															0
Forfeited (in units)															0
Balance at the end of the period (in units or shares)							1,333,334				1,333,334				1,333,334	1,333,334
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)										$ 9.30					$ 9.30
Granted (in dollars per share)															0
Vested (in dollars per share)															0
Forfeited (in dollars per share)															0
Balance at the end of the period (in dollars per share)							$ 9.30				$ 9.30				$ 9.30	$ 9.30
Unrecognized compensation expenses							$ 7.3								$ 7.3
Weighted average period of compensation expense expected to be recognized															2 years 2 months 12 days
Third Anniversary of Grant Date | Restricted units
Equity compensation
Annual award vesting percentage															33.33%
Third Anniversary of Grant Date | Restricted units with a market condition
Equity compensation
Granted (in units)					666,667
Units
Granted (in units)					666,667
Weighted Average Grant Date Fair Value
Balance at the end of the period (in dollars per share)					$ 10.92	$ 10.92
First Anniversary of Grant Date | Restricted units
Equity compensation
Annual award vesting percentage															25.00%
First Anniversary of Grant Date | Restricted units with a market condition
Equity compensation
Granted (in units)					666,667
Units
Granted (in units)					666,667
Weighted Average Grant Date Fair Value
Balance at the end of the period (in dollars per share)					$ 7.68	$ 7.68