CAPITAL STOCK - Summary of Dividend Distribution Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Dividends Payable [Line Items]
Distributions declared to common stockholders	$ 1,285,124	$ 1,516,323
Distributions declared per common share (in dollars per share)	$ 0.91	$ 1.05
Distributions paid to common stockholders after period end	$ 307,613	$ 357,527
Distributions paid per common share after period end (in dollars per share)	$ 0.22	$ 0.25
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 0	$ 7,414
Preferred series dividends declared (in dollars per share)	$ 0	$ 1.060
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 34,500	$ 34,500
Preferred series dividends declared (in dollars per share)	$ 1.875	$ 1.875
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 50,040	$ 50,040
Preferred series dividends declared (in dollars per share)	$ 1.738	$ 1.738
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 27,625	$ 27,624
Preferred series dividends declared (in dollars per share)	$ 1.625	$ 1.625
Series H Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 0	$ 1,862
Preferred series dividends declared (in dollars per share)	$ 0	$ 0.846
Series I Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 29,871	$ 15,135
Preferred series dividends declared (in dollars per share)	$ 1.688	$ 0.86