CAPITAL STOCK - Summary of Dividend Distribution Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Dividends Payable [Line Items]
Distributions declared to common stockholders	$ 364,266	$ 349,300	$ 798,893	$ 697,197
Distributions declared per common share (in dollars per share)	$ 0.25	$ 0.30	$ 0.55	$ 0.60
Distributions paid to common stockholders after period end	$ 364,066	$ 349,300	$ 364,066	$ 349,300
Distributions paid per common share after period end (in dollars per share)	$ 0.25	$ 0.30	$ 0.25	$ 0.30
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 3,336	$ 3,336	$ 6,672	$ 7,652
Preferred series dividends declared (in dollars per share)	$ 0.477	$ 0.477	$ 0.953	$ 0.953
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 8,625	$ 8,625	$ 17,250	$ 17,250
Preferred series dividends declared (in dollars per share)	$ 0.469	$ 0.469	$ 0.938	$ 0.938
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 0	$ 0	$ 0	$ 2,253
Preferred series dividends declared (in dollars per share)	$ 0	$ 0	$ 0	$ 0.196
Series F Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 12,510	$ 12,510	$ 25,020	$ 25,020
Preferred series dividends declared (in dollars per share)	$ 0.434	$ 0.434	$ 0.869	$ 0.869
Series G Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 6,906	$ 6,906	$ 13,812	$ 12,968
Preferred series dividends declared (in dollars per share)	$ 0.406	$ 0.406	$ 0.813	$ 0.763
Series H Preferred Stock
Dividends Payable [Line Items]
Preferred dividends declared	$ 745	$ 0	$ 1,862	$ 0
Preferred series dividends declared (in dollars per share)	$ 0.339	$ 0	$ 0.846	$ 0