Consolidated Statements of Changes in Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common distributions declared per share	$ 1.040	$ 0.94	$ 0.88
Preferred Stock
Redemption of 6.75% Series G Cumulative Redeemable Shares, Shares	0		3,264,362
6.75% Series G Cumulative Redeemable Preferred Stock
Preferred stock distributions declared	$ 0	$ 0	$ 0.5671875
Redemption of 6.75% Series G Cumulative Redeemable Shares, Shares			3,264,362
8.00% Series E Cumulative Convertible Preferred Stock
Preferred stock distributions declared	$ 1.3288	$ 1.3288	$ 1.3288