CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Common dividends declared, per share	$ 2.05	$ 2.44	$ 2.65
7.875% Series A Cumulative Redeemable Preferred Stock [Member]
Preferred series dividends declared, per share	$ 1.97	$ 1.97	$ 1.97
6.00% Series B Cumulative Convertible Preferred Stock [Member]
Preferred series dividends declared, per share	$ 0.375	$ 1.50	$ 1.50
7.625% Series C Cumulative Redeemable Preferred Stock [Member]
Preferred series dividends declared, per share	$ 1.19
7.50% Series D Cumulative Redeemable Preferred Stock [Member]
Preferred series dividends declared, per share	$ 0.56