CAPITAL STOCK - Summary of Dividend Distribution Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Dividends Payable [Line Items]
Distributions declared to common stockholders	$ 1,516,323,000	$ 1,457,007,000
Distributions declared per common share (in dollars per share)	$ 1.05	$ 1.20
Distributions paid to common stockholders after period end	$ 357,527,000	$ 394,129,000
Distributions paid per common share after period end (in dollars per share)	$ 0.25	$ 0.30
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 7,414,000	$ 14,323,000
Preferred series dividends declared (in dollars per share)	$ 1.060	$ 1.906
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 34,500,000	$ 34,500,000
Preferred series dividends declared (in dollars per share)	$ 1.875	$ 1.875
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 0	$ 2,253,000
Preferred series dividends declared (in dollars per share)	$ 0	$ 0.196
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 50,040,000	$ 50,040,000
Preferred series dividends declared (in dollars per share)	$ 1.738	$ 1.738
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 27,624,000	$ 26,781,000
Preferred series dividends declared (in dollars per share)	$ 1.625	$ 1.575
Series H Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 1,862,000	$ 1,415,000
Preferred series dividends declared (in dollars per share)	$ 0.846	$ 0.643
Series I Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 15,135,000	$ 0
Preferred series dividends declared (in dollars per share)	$ 0.858	$ 0