EQUITY COMPENSATION (Restricted Units) (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended		9 Months Ended
	Sep. 16, 2019	Jun. 14, 2019	Mar. 15, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
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	$ 0.28	$ 0.96	$ 1.05
Distribution equivalents made to holders						$ 16.1
Weighted Average Grant Date Fair Value
Unrecognized compensation expenses				$ 83.1		$ 83.1
Restricted units
Equity compensation
Distribution equivalents made to holders				$ 5.3
Units
Balance at the beginning of the period (in units or shares)						16,255,475
Granted (in units)						4,202,622
Vested (in units)						(3,579,050)
Forfeited (in units)						(234,035)
Balance at the end of the period (in units or shares)				16,645,012		16,645,012
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)						$ 19.21
Granted (in dollars per share)						20.61
Vested (in dollars per share)						17.95
Forfeited (in dollars per share)						19.33
Balance at the end of the period (in dollars per share)				$ 19.83		$ 19.83
Unrecognized compensation expenses				$ 216.2		$ 216.2
Weighted average period of compensation expense expected to be recognized						2 years 11 months 4 days
Restricted units with a market condition
Units
Balance at the beginning of the period (in units or shares)						1,333,334
Granted (in units)						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
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)						$ 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
Unrecognized compensation expenses				$ 8.2		$ 8.2
Weighted average period of compensation expense expected to be recognized						2 years 5 months 4 days
Third Anniversary of Grant Date | Restricted units
Equity compensation
Annual award vesting percentage						33.33%
First Anniversary of Grant Date | Restricted units
Equity compensation
Annual award vesting percentage						25.00%