Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In-Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Noncontrolling Interests	Series C Preferred Stock Preferred Stock	Series D Preferred Stock Preferred Stock	Series I Preferred Stock Preferred Stock
Balance at Dec. 31, 2009	$ 4,913,129	$ 809	$ 3,525,901	$ (302,705)	$ (33,538)	$ 949,669	$ 524,691	$ 151,981	$ 96,321
Balance (in shares) at Dec. 31, 2009		77,515,000
Increase (Decrease) in Stockholders' Equity
Net income	314,582					300,575	14,007
Other comprehensive income	10,879				10,879
Preferred dividends	(29,749)					(29,749)
Redemption of units and DRIP proceeds	23,344	5	23,339
Redemption of units and DRIP proceeds (in shares)		470,000
Reallocation of noncontrolling interest in the operating partnership	(18,948)					(18,948)
Deferred compensation plan and stock award, net	20	2	535	(517)
Deferred compensation plan and stock award, net (in shares)		212,000
Amortization of deferred compensation plan	31,741		31,741
Deconsolidation of real estate investments	(6,521)					3,011	(9,532)
Net proceeds from preferred stock offering	122,041							122,041
Equity component of convertible notes	76,039		76,039
Proceeds from stock options exercised	3,288	1	3,287
Proceeds from stock options exercised (in shares)		110,000
Cash contributions from noncontrolling interests	2,788						2,788
Cash distributions to noncontrolling interests	(13,494)						(13,494)
Cash distribution declared ($1.08, $0.55 and $0.40 per common share, none of which represented a return of capital for federal income tax purposes for the year ended December 31, 2012, 2011 and 2010, respectively)	(31,595)					(31,595)
Balance at Dec. 31, 2010	5,397,544	817	3,660,842	(303,222)	(22,659)	1,172,963	518,460	274,022	96,321
Balance (in shares) at Dec. 31, 2010		78,307,000
Increase (Decrease) in Stockholders' Equity
Net income	662,493					647,410	15,083
Other comprehensive income	(5,786)				(5,786)
Preferred dividends	(30,178)					(30,178)
Redemption of units and DRIP proceeds	898		898
Redemption of units and DRIP proceeds (in shares)		13,000
Reallocation of noncontrolling interest in the operating partnership	(39,040)					(39,040)
Deferred compensation plan and stock award, net	(4,787)	3	696	(5,486)
Deferred compensation plan and stock award, net (in shares)		262,000
Amortization of deferred compensation plan	33,252		33,252
Proceeds from issuance of common stock	531,306	70	531,236
Proceeds from issuance of common stock (in shares)		6,957,000
Proceeds from stock options exercised	10,037	2	10,035
Proceeds from stock options exercised (in shares)		244,000
Consolidation of joint venture interest	87,798						87,798
Cash distributions to noncontrolling interests	(143,579)						(143,579)
Cash distribution declared ($1.08, $0.55 and $0.40 per common share, none of which represented a return of capital for federal income tax purposes for the year ended December 31, 2012, 2011 and 2010, respectively)	(46,649)					(46,649)
Balance at Dec. 31, 2011	6,453,309	892	4,236,959	(308,708)	(28,445)	1,704,506	477,762	274,022	96,321
Balance (in shares) at Dec. 31, 2011		85,783,000
Increase (Decrease) in Stockholders' Equity
Net income	201,996					196,405	5,591
Other comprehensive income	(1,142)				(1,142)
Preferred dividends	(30,411)					(30,411)
Redemption of units and DRIP proceeds	99,570	13	99,557
Redemption of units and DRIP proceeds (in shares)		1,305,000
Conversion of units of the Operating Partnership to common stock	87,513	11	87,502
Conversion of units of the Operating Partnership to common stock (in shares)		1,096,000
Redemption of preferred stock	(200,013)					(10,010)		(93,682)	(96,321)
Reallocation of noncontrolling interest in the operating partnership	(61,238)					(61,238)
Deferred compensation plan and stock award, net	(13,428)	3	719	(14,150)
Deferred compensation plan and stock award, net (in shares)		43,000
Amortization of deferred compensation plan	28,742		28,742
Net proceeds from preferred stock offering	221,965									221,965
Proceeds from issuance of common stock	201,279	27	201,252
Proceeds from issuance of common stock (in shares)		2,640,000
Proceeds from stock options exercised	13,173	4	13,169
Proceeds from stock options exercised (in shares)		383,000
Consolidation of joint venture interest	25,894						25,894
Cash distributions to noncontrolling interests	(21,946)						(21,946)
Cash distribution declared ($1.08, $0.55 and $0.40 per common share, none of which represented a return of capital for federal income tax purposes for the year ended December 31, 2012, 2011 and 2010, respectively)	(98,160)					(98,160)
Balance at Dec. 31, 2012	$ 6,907,103	$ 950	$ 4,667,900	$ (322,858)	$ (29,587)	$ 1,701,092	$ 487,301	$ 180,340		$ 221,965
Balance (in shares) at Dec. 31, 2012	91,249,632	91,250,000