SUBSEQUENT EVENTS (Details) - $ / shares			12 Months Ended
	Jan. 24, 2017	Jan. 01, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Awards | Performance-Based
Subsequent events
Vested (in shares)			113,903	184,666
9.25% Series A Preferred Stock
Subsequent events
Preferred stock, dividend rate (as a percent)			9.25%	9.25%
7.875% Series B Preferred Stock
Subsequent events
Preferred stock, dividend rate (as a percent)			7.875%	7.875%
7.125% Series C Preferred Stock
Subsequent events
Preferred stock, dividend rate (as a percent)			7.125%	7.125%
6.45% Series D Preferred Stock
Subsequent events
Preferred stock, dividend rate (as a percent)			6.45%
Subsequent events
Subsequent events
Cash dividends declared, common stock (in dollars per share)	$ 0.1625
Subsequent events | Restricted Stock Awards | Performance-Based
Subsequent events
Vested (in shares)		39,959
Subsequent events | 7.875% Series B Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share)	0.4921875
Subsequent events | 7.125% Series C Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share)	0.4453125
Subsequent events | 6.45% Series D Preferred Stock
Subsequent events
Cash dividends declared, preferred stock (in dollars per share)	$ 0.403125