EQUITY - Narrative (Details)				9 Months Ended		12 Months Ended
		Jul. 01, 2018 USD ($) vote	Jan. 16, 2018	Sep. 30, 2018 USD ($) series $ / shares shares		Dec. 31, 2015	Jun. 30, 2018 $ / shares	Dec. 31, 2017 USD ($)	[1]	Jun. 20, 2016 shares	Mar. 17, 2016 shares
Class of Stock [Line Items]
Preferred stock dividend rate (as a percent)			7.375%
Authorized capital stock (in shares)				5,000,000,000
Preferred stock, shares authorized (in shares)				1,000,000,000
Retained Earnings | $		$ 0		$ 551,036,000	[1]			$ 0
Preferred stock, number of series designated | series				2
Preferred stock, shares issued (in shares)	[1]			20,000,000
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares				$ 25.00
Preferred stock, change of control event, redemption price per share (in dollars per share) | $ / shares				$ 25.25
Preferred stock, change of control event, increase in dividend rate, percentage				5.00%
Percentage of carried interest received by general partners (up to)						1.00%
Class A Common Stock
Class of Stock [Line Items]
Common stock, conversion ratio		1
Common stock, par value (in dollars per share) | $ / shares							$ 0.01
Common stock, shares authorized (in shares)				3,500,000,000
Class B Common Stock
Class of Stock [Line Items]
Common stock, conversion ratio		1
Common stock, par value (in dollars per share) | $ / shares							0.01
Common stock, shares authorized (in shares)				1
Common stock, number of votes per share | vote		1
Class C Common Stock
Class of Stock [Line Items]
Common stock, conversion ratio		1
Common stock, par value (in dollars per share) | $ / shares							$ 0.01
Common stock, shares authorized (in shares)				499,999,999
Series A Preferred Units/Preferred Stock
Class of Stock [Line Items]
Preferred stock dividend rate (as a percent)				6.75%
Preferred stock, conversion ratio		1
Preferred stock, par value (in dollars per share) | $ / shares				$ 0.01
Preferred stock, shares authorized (in shares)				13,800,000
Preferred stock, shares issued (in shares)											13,800,000
Preferred stock, redemption price per share (in dollars per share) | $ / shares				$ 25.00
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividend rate (as a percent)				6.50%
Preferred stock, conversion ratio		1
Preferred stock, par value (in dollars per share) | $ / shares				$ 0.01
Preferred stock, shares authorized (in shares)				6,200,000
Preferred stock, shares issued (in shares)										6,200,000
Preferred stock, redemption price per share (in dollars per share) | $ / shares				$ 25.00

[1] See Note 1 "Organization."