CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) (Parenthetical) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Dividends declared per share of common stock (in dollars per share)	$ 0.3	$ 0.30
7.875% Series A Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.875%	7.875%	7.875%
Preferred series dividends declared, per share (in dollars per share)	$ 0	$ 0.492
7.625% Series C Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.625%	7.625%	7.625%
Preferred series dividends declared, per share (in dollars per share)	$ 0.477	$ 0.477
7.50% Series D Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.50%	7.50%	7.50%
Preferred series dividends declared, per share (in dollars per share)	$ 0.469	$ 0.469
7.625% Series E Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.625%	7.625%	7.625%
Preferred series dividends declared, per share (in dollars per share)	$ 0.196	$ 0.477
6.95% Series F Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	6.95%	6.95%	6.95%
Preferred series dividends declared, per share (in dollars per share)	$ 0.434	$ 0
6.50% Series G Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	6.50%	6.50%	6.50%
Preferred series dividends declared, per share (in dollars per share)	$ 0.357	$ 0