Consolidated Statements of Capital (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Increase (Decrease) in Stockholders' Equity
Balance	$ 6,648,339	$ 5,481,882	$ 4,997,747
Net income	207,593	677,122	319,156
Other comprehensive income (loss)	(1,530)	(6,077)	9,818
Preferred distributions	(30,411)	(30,178)	(29,749)
Issuance of common units	42,239	60,443	2,874
Redemption of units and DRIP proceeds	99,570	32	(1,760)
Redemption of preferred units	(200,013)
Deferred compensation plan and stock award, net	(13,428)	(4,787)	20
Amortization of deferred compensation plan	28,742	33,252	31,741
Deconsolidation of real estate investments			(6,521)
Consolidation of real estate investments	25,894	86,797
Equity component of convertible notes			76,039
Contributions - net proceeds from preferred stock offering	221,965		122,041
Contributions - net proceeds from common stock offering	201,279	531,306
Contributions - proceeds from stock options exercised	13,173	10,037	3,288
Contributions from noncontrolling interests			2,788
Distributions to noncontrolling interests	(21,946)	(143,579)	(13,494)
Cash distribution declared ($1.08,$0.55,and $0.40 per common unit, none of which represented a return of capital for federal income tax purposes for the year ended 2012,2011 and 2010 respectively)	(101,456)	(47,911)	(32,106)
Balance	7,120,010	6,648,339	5,481,882
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity
Balance	(29,119)	(23,042)	(32,860)
Other comprehensive income (loss)	(1,530)	(6,077)	9,818
Balance	(30,649)	(29,119)	(23,042)
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity
Balance	477,762	518,460	524,691
Net income	5,591	15,083	14,007
Deconsolidation of real estate investments			(9,532)
Consolidation of real estate investments	25,894	87,798
Contributions from noncontrolling interests			2,788
Distributions to noncontrolling interests	(21,946)	(143,579)	(13,494)
Balance	487,301	477,762	518,460
General Partner | Common Units
Increase (Decrease) in Stockholders' Equity
Balance	5,714,856	4,573,565	4,196,891
Balance (in units)	85,783,000	78,307,000	77,515,000
Net income	165,994	617,232	270,826
Redemption of units and DRIP proceeds	99,570	898	23,344
Redemption of units and DRIP proceeds (in units)	1,305,000	13,000	470,000
Redemption of units	87,513
Redemption of units (in units)	1,096,000
Redemption of preferred units	(10,010)
Deferred compensation plan and stock award, net	(13,428)	(4,787)	20
Deferred compensation plan & stock award, net (in units)	43,000	262,000	212,000
Amortization of deferred compensation plan	28,742	33,252	31,741
Deconsolidation of real estate investments			3,011
Equity component of convertible notes			76,039
Contributions - net proceeds from common stock offering	201,279	531,306
Contributions - net proceeds from common stock offering (in units)	2,640,000	6,957,000
Contributions - proceeds from stock options exercised	13,173	10,037	3,288
Contributions - proceeds from stock options exercised (in units)	383,000	244,000	110,000
Cash distribution declared ($1.08,$0.55,and $0.40 per common unit, none of which represented a return of capital for federal income tax purposes for the year ended 2012,2011 and 2010 respectively)	(98,160)	(46,647)	(31,595)
Balance	6,189,529	5,714,856	4,573,565
Balance (in units)	91,250,000	85,783,000	78,307,000
Limited Partners | Common Units
Increase (Decrease) in Stockholders' Equity
Balance	114,497	42,556	60,723
Balance (in units)	2,765,000	1,249,000	1,684,000
Net income	5,597	14,629	4,574
Issuance of common units	42,239	60,443	2,874
Issuance of common units (in units)	801,000	1,530,000	45,000
Redemption of units and DRIP proceeds		(866)	(25,104)
Redemption of units and DRIP proceeds (in units)		(12,000)	(285,000)
Redemption of units	(87,513)
Redemption of units (in units)	(1,096,000)
Deferred compensation plan & stock award, net (in units)	290,000	(2,000)	(195,000)
Consolidation of real estate investments		(1,001)
Cash distribution declared ($1.08,$0.55,and $0.40 per common unit, none of which represented a return of capital for federal income tax purposes for the year ended 2012,2011 and 2010 respectively)	(3,296)	(1,264)	(511)
Balance	71,524	114,497	42,556
Balance (in units)	2,760,000	2,765,000	1,249,000
Series C Preferred Units
Increase (Decrease) in Stockholders' Equity
Balance	274,022	274,022	151,981
Net income	20,290	22,300	21,873
Preferred distributions	(20,290)	(22,300)	(21,873)
Redemption of preferred units	(93,682)
Contributions - net proceeds from preferred stock offering			122,041
Balance	180,340	274,022	274,022
Series D Preferred Units
Increase (Decrease) in Stockholders' Equity
Balance	96,321	96,321	96,321
Net income	4,266	7,878	7,876
Preferred distributions	(4,266)	(7,878)	(7,876)
Redemption of preferred units	(96,321)
Balance		96,321	96,321
Series I Preferred Units
Increase (Decrease) in Stockholders' Equity
Net income	5,855
Preferred distributions	(5,855)
Contributions - net proceeds from preferred stock offering	221,965
Balance	$ 221,965