SUBSEQUENT EVENTS (Details) $ / shares in Units, $ in Millions			12 Months Ended
	Jan. 29, 2021 $ / shares	Jan. 15, 2021 director	Dec. 31, 2020 director	Dec. 31, 2019	Jan. 07, 2021 USD ($)
Subsequent events
Number of board of directors | director			6
6.45% Series D Preferred Stock
Subsequent events
Preferred stock, dividend rate			6.45%	6.45%
6.25% Series E Preferred Stock
Subsequent events
Preferred stock, dividend rate			6.25%	6.25%
Subsequent events
Subsequent events
Number of board of directors | director		7
Subsequent events | 6.45% Series D Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share) | $ / shares	$ 0.403125
Preferred stock, dividend rate	6.45%
Subsequent events | 6.25% Series E Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share) | $ / shares	$ 0.390625
Preferred stock, dividend rate	6.25%
Convertible Debt | 1.50% convertible senior notes due 2026 | Subsequent events
Subsequent events
Debt aggregate principal amount | $					$ 287.5
Stated interest rate					1.50%