EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended	12 Months Ended
	Mar. 20, 2018	Sep. 30, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock, shares authorized		500,000,000	500,000,000
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Preferred stock, shares authorized		100,000,000	100,000,000
Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01
General partner, ownership interest		51.00%
Undesignated preferred stock
Class of Stock [Line Items]
Preferred stock, shares authorized		90,600,000
7.125% Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate	7.125%
Payments for repurchase of redeemable preferred shares	$ 85.3
Preferred stock, shares outstanding	3,400,000
Preferred stock, redemption price (in dollars per share)	$ 25
Preferred stock, liquidation preference (in dollars per share)		$ 25
6.45% Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized		3,000,000
Preferred stock, dividend rate		6.45%	6.45%
Preferred stock, shares outstanding		3,000,000	3,000,000
Preferred stock, liquidation preference (in dollars per share)		$ 25
Annual dividend rate per share (in dollars per share)		$ 1.6125
6.45% Series D Preferred Stock | Maximum
Class of Stock [Line Items]
Ratio for conversion		3.9216
6.25% Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized		6,400,000
Preferred stock, dividend rate		6.25%	6.25%
Preferred stock, shares outstanding		6,400,000	6,400,000
Preferred stock, liquidation preference (in dollars per share)		$ 25
Annual dividend rate per share (in dollars per share)		$ 1.5625
6.25% Series E Preferred Stock | Maximum
Class of Stock [Line Items]
Ratio for conversion		3.1686
Operating partnership | Non-controlling Interests
Class of Stock [Line Items]
Number of common units of operating partnership owned by unaffiliated third parties (in shares)		213,189	259,265
Limited partner, ownership percentage		1.00%	1.00%
GIC
Class of Stock [Line Items]
Limited partner, ownership percentage		49.00%
Unaffiliated Third Parties | Operating partnership
Class of Stock [Line Items]
Limited partner capital account units conversion ratio		1