Condensed Consolidated Statements of Changes in Equity (Unaudited) (USD $) In Thousands	Accumulated Distributions in Excess of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Interest Rate Swap [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member] Common Stock [Member]	Additional Paid-in Capital [Member] Preferred Stock [Member]	Additional Paid-in Capital [Member]	Parent [Member] Interest Rate Swap [Member]	Parent [Member] Common Stock [Member]	Parent [Member] Preferred Stock [Member]	Parent [Member]	Noncontrolling Interest [Member]	Interest Rate Swap [Member]	Common Stock [Member]	Preferred Stock [Member]	Total
Balance at Dec. 31, 2011	$ (702,999)		$ (107,660)		$ 954		$ 4,069			$ 5,492,022				$ 4,686,386	$ 193,757				$ 4,880,143
Balance (in Shares) at Dec. 31, 2011					954		406,938
Contributions from noncontrolling interests															1,201				1,201
Net income	122,750													122,750	8,785				131,535
Change in unrealized gain on marketable securities			928											928					928
Change in unrealized gain on interest rate swaps		372									372					372
Change in foreign currency translation adjustment			6,471											6,471	3,101				9,572
Redeemable noncontrolling interests															(3,148)				(3,148)
Dividends	(191,033)													(191,033)					(191,033)
Distributions to noncontrolling interests															(8,823)				(8,823)
Issuance of stock				16		11		18,055	387,214			18,066	387,230				18,066	387,230	18,066
Issuance of stock (in Shares)				16		1,093
Surrender of restricted stock																			(1,555)
Exercise of common stock options							5			7,174				7,179					7,179
Exercise of common stock options (in Shares)							480
Acquisition of noncontrolling interests										(1,244)				(1,244)	(4,392)				(5,636)
Amortization of equity awards										8,016				8,016					8,016
Surrender of common stock										(1,555)				(1,555)					(1,555)
Surrender of common stock (in Shares)							(84)
Repurchase of common stock							(16)			(28,942)				(28,958)					(28,958)
Repurchase of common stock (in Shares)							(1,536)
Balance at Jun. 30, 2012	(771,282)		(99,889)		970		4,069			5,880,740				5,014,608	190,481				5,205,089
Balance (in Shares) at Jun. 30, 2012					970		406,891
Balance at Mar. 31, 2012
Net income																			72,387
Change in unrealized gain on marketable securities																			(231)
Change in unrealized gain on interest rate swaps																179
Balance at Jun. 30, 2012					970														5,205,089
Balance (in Shares) at Jun. 30, 2012					970
Balance at Dec. 31, 2012	(824,008)		(66,182)		102		4,078			5,651,170				4,765,160	167,320				4,932,480
Balance (in Shares) at Dec. 31, 2012					102		407,782
Contributions from noncontrolling interests															858				858
Net income	118,909													118,909	4,871				123,780
Change in unrealized gain on marketable securities			6,228											6,228					6,228
Change in foreign currency translation adjustment			(1,844)											(1,844)	(660)				(2,504)
Redeemable noncontrolling interests															(3,222)				(3,222)
Dividends	(200,971)													(200,971)					(200,971)
Distributions to noncontrolling interests															(5,063)				(5,063)
Issuance of stock						5		9,208				9,213					9,213		9,213
Issuance of stock (in Shares)						560
Surrender of restricted stock							(2)			(3,174)				(3,176)					(3,176)
Surrender of restricted stock (in Shares)							(212)
Exercise of common stock options							15			27,927				27,942					27,942
Exercise of common stock options (in Shares)							1,487
Acquisition of noncontrolling interests										(5,430)				(5,430)	(20,096)				(25,526)
Amortization of equity awards										6,242				6,242					6,242
Balance at Jun. 30, 2013	$ (906,070)		$ (61,798)		$ 102		$ 4,096			$ 5,685,943				$ 4,722,273	$ 144,008				$ 4,866,281
Balance (in Shares) at Jun. 30, 2013					102		409,617