SUBSEQUENT EVENTS (Details) - $ / shares		12 Months Ended
	Jan. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
6.45% Series D Preferred Stock
Subsequent events
Preferred stock, dividend rate (as a percent)		6.45%	6.45%
6.25% Series E Preferred Stock
Subsequent events
Preferred stock, dividend rate (as a percent)		6.25%	6.25%
Subsequent events
Subsequent events
Cash dividends declared, common stock (in dollars per share)	$ 0.18
Subsequent events | 6.45% Series D Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share)	0.403125
Subsequent events | 6.25% Series E Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share)	$ 0.390625