CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, unless otherwise specified	Total	Total Stockholders' Equity	Preferred Stock	Common Stock	Additional Paid-In Capital	Cumulative Dividends In Excess Of Earnings	Accumulated Other Comprehensive Income (Loss)	Total Noncontrolling Interests
Balance at Dec. 31, 2011	$ 9,220,622	$ 9,033,482	$ 285,173	$ 408,629	$ 9,383,536	$ (1,024,274)	$ (19,582)	$ 187,140
Balance (in shares) at Dec. 31, 2011			11,820	408,629
Increase (Decrease) in Stockholders' Equity
Net income	196,564	193,380				193,380		3,184
Other comprehensive income (loss)	1,916	1,916					1,916
Preferred stock redemption	(296,896)	(296,896)	(285,173)			(11,723)
Preferred stock redemption (in shares)			(11,820)
Issuance of common stock, net	366,922	367,956		9,559	358,397			(1,034)
Issuance of common stock, net (in shares)				9,559
Repurchase of common stock	(6,984)	(6,984)		(167)	(6,817)
Repurchase of common stock (in shares)				(167)
Exercise of stock options	37,631	37,631		1,412	36,219
Exercise of stock options (in shares)	1,412			1,412
Amortization of deferred compensation	5,373	5,373			5,373
Preferred dividends	(5,283)	(5,283)				(5,283)
Common dividends ($0.525 and $0.50 per share for the period ended March 31, 2013 and 2012, respectively)	(205,784)	(205,784)				(205,784)
Distributions to noncontrolling interests	(3,912)							(3,912)
Issuance of noncontrolling interests	181							181
Purchase of noncontrolling interests	(388)							(388)
Balance at Mar. 31, 2012	9,309,962	9,124,791		419,433	9,776,708	(1,053,684)	(17,666)	185,171
Balance (in shares) at Mar. 31, 2012				419,433
Balance at Dec. 31, 2012	10,753,777	10,551,237		453,191	11,180,066	(1,067,367)	(14,653)	202,540
Balance (in shares) at Dec. 31, 2012				453,191
Increase (Decrease) in Stockholders' Equity
Net income	233,784	230,585				230,585		3,199
Other comprehensive income (loss)	(1,951)	(1,951)					(1,951)
Issuance of common stock, net	12,277	14,456		555	13,901			(2,179)
Issuance of common stock, net (in shares)				555
Repurchase of common stock	(689)	(689)		(14)	(675)
Repurchase of common stock (in shares)				(14)
Exercise of stock options	20,665	20,665		685	19,980
Exercise of stock options (in shares)	796			685
Amortization of deferred compensation	5,430	5,430			5,430
Common dividends ($0.525 and $0.50 per share for the period ended March 31, 2013 and 2012, respectively)	(238,467)	(238,467)				(238,467)
Distributions to noncontrolling interests	(3,754)							(3,754)
Issuance of noncontrolling interests	987							987
Balance at Mar. 31, 2013	$ 10,782,059	$ 10,581,266		$ 454,417	$ 11,218,702	$ (1,075,249)	$ (16,604)	$ 200,793
Balance (in shares) at Mar. 31, 2013				454,417