CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Common dividends declared, per share	$ 0.45	$ 0.55
6.00% Series B Cumulative Convertible Preferred Stock
Preferred series dividends declared, per share		$ 0.375
7.875% Series A Cumulative Redeemable Preferred Stock
Preferred series dividends declared, per share	$ 0.492	$ 0.492
7.625% Series C Cumulative Redeemable Preferred Stock
Preferred series dividends declared, per share	$ 0.477
7.50% Series D Cumulative Redeemable Preferred Stock
Preferred series dividends declared, per share	$ 0.469