COMMON STOCK AND PREFERRED STOCK - Summary of Dividend Distribution Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Distributions declared to common stockholders	$ 1,285,701	$ 1,162,897	$ 1,133,768
Distributions declared per common share (in dollars per share)	$ 1.2	$ 1.2	$ 1.2
Distributions paid to common stockholders after period end	$ 347,876	$ 305,674
Distributions paid per common share after period end (in dollars per share)	$ 0.3	$ 0.3
7.875% Series A Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 9,527	$ 14,593	$ 14,593
Preferred series dividends declared (in dollars per share)	$ 1.285	$ 1.969	$ 1.969
7.625% Series C Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 22,875	$ 22,875	$ 22,875
Preferred series dividends declared (in dollars per share)	$ 1.906	$ 1.906	$ 1.906
7.50% Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 34,500	$ 34,500	$ 34,500
Preferred series dividends declared (in dollars per share)	$ 1.875	$ 1.875	$ 1.875
7.625% Series E Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 21,922	$ 10,292
Preferred series dividends declared (in dollars per share)	$ 1.906	$ 0.953
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 20,811	$ 0
Preferred series dividends declared (in dollars per share)	$ 0.724	$ 0