EQUITY - Narrative (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2016 $ / shares shares	Dec. 31, 2015 $ / shares shares
Equity
Common stock, shares authorized | shares	500,000,000	500,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized | shares	100,000,000	100,000,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Undesignated preferred stock
Equity
Preferred stock, shares authorized | shares	91,600,000
9.25% Series A Preferred Stock
Equity
Preferred stock, shares authorized | shares	2,000,000	2,000,000
Preferred stock, dividend rate (as a percent)	9.25%	9.25%
Preferred stock, liquidation preference (in dollars per share)	$ 25
Annual dividend rate per share (in dollars per share)	$ 2.3125
9.25% Series A Preferred Stock | Maximum
Equity
Ratio for conversion	5.92417
7.875% Series B Preferred Stock
Equity
Preferred stock, shares authorized | shares	3,000,000	3,000,000
Preferred stock, dividend rate (as a percent)	7.875%	7.875%
Preferred stock, liquidation preference (in dollars per share)	$ 25
Annual dividend rate per share (in dollars per share)	$ 1.96875
7.875% Series B Preferred Stock | Maximum
Equity
Ratio for conversion	5.6497
7.125% Series C Preferred Stock
Equity
Preferred stock, shares authorized | shares	3,400,000	3,400,000
Preferred stock, dividend rate (as a percent)	7.125%	7.125%
Preferred stock, liquidation preference (in dollars per share)	$ 25
Annual dividend rate per share (in dollars per share)	$ 1.78125
7.125% Series C Preferred Stock | Maximum
Equity
Ratio for conversion	5.1440
Operating partnership | Non-controlling Interests in Operating Partnership
Equity
Number of common units of operating partnership owned by unaffiliated third parties | shares	484,979	516,021
Percentage of limited partnership interest in operating partnership	1.00%	1.00%