CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividends declared per share of common stock	$ 1.2	$ 1.5	$ 2.05
6.00% Series B Cumulative Convertible Preferred Stock
Preferred series dividends declared, per share			$ 0.375
7.625% Series C Cumulative Redeemable Preferred Stock
Preferred series dividends declared, per share	$ 1.91	$ 1.91	$ 1.19
7.50% Series D Cumulative Redeemable Preferred Stock
Preferred series dividends declared, per share			$ 0.56
7.875% Series A Cumulative Redeemable Preferred Stock
Preferred series dividends declared, per share	$ 1.97	$ 1.97	$ 1.97
Series D Preferred Stock
Preferred series dividends declared, per share	$ 1.88	$ 1.88