Redeemable Noncontrolling Interests (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Redeemable Noncontrolling Interest Units Table [Abstract]
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	$ 934,677	$ 1,066,974
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	226,000	261,000
Redeemable Noncontrolling Interests Rollforward [Abstract]
Reedemable Noncontrolling Interest, Beginning Balance	1,327,974	1,251,628
Net Income	55,912	55,228
Distributions	(50,865)	(53,515)
Conversion of Class A redeemable units into common shares, at redemption value	(64,830)	(126,764)
Adjustment to carry Class A redeemable units at redemption value	(98,092)	191,826
Cumulative Redeemable Preferred Units Redemption Amount	(28,000)	(13,000)
Other, net	18,578	22,571
Reedemable Noncontrolling Interest, Ending Balance	1,160,677	1,327,974
Redeemable Noncontrolling Interests Additional Disclosure [Abstract]
Fair value of Series G convertible preferred units and Series D-13 cumulative redeemable preferred units	54,865	55,097
Cumulative Redeemable Preferred Units Redemption Amount	28,000	13,000
Common Class A [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Outstanding Partnership Units held by Third Parties	12,160,771	12,804,202
Preference Or Annual Distribution Rate	$ 2.76
Series D10 Cumulative Redeemable Preferred Unit [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Dividend Percentage	7.00%
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	80,000	80,000
Outstanding Partnership Units held by Third Parties	3,200,000	3,200,000
Par or Stated Value Per Share	$ 25.00
Preference Or Annual Distribution Rate	$ 1.75
Series D11 Cumulative Redeemable Preferred Unit [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Dividend Percentage	7.20%
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	0	35,000
Outstanding Partnership Units held by Third Parties	0	1,400,000
Par or Stated Value Per Share	$ 25.00
Preference Or Annual Distribution Rate	$ 1.80
Redeemable Noncontrolling Interests Rollforward [Abstract]
Cumulative Redeemable Preferred Units Redemption Amount	(28,000)
Redeemable Noncontrolling Interests Additional Disclosure [Abstract]
Redemption Price per share	$ 20.00
Cumulative Redeemable Preferred Units Redemption Amount	28,000
Series D14 Cumulative Redeemable Preferred Unit [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Dividend Percentage	6.75%
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	100,000	100,000
Outstanding Partnership Units held by Third Parties	4,000,000	4,000,000
Par or Stated Value Per Share	$ 25.00
Preference Or Annual Distribution Rate	$ 1.6875
Series D15 Cumulative Redeemable Preferred Unit [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Dividend Percentage	6.875%
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	45,000	45,000
Outstanding Partnership Units held by Third Parties	1,800,000	1,800,000
Par or Stated Value Per Share	$ 25.00
Preference Or Annual Distribution Rate	$ 1.71875
Series D16 Cumulative Redeemable Preferred Unit [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Dividend Percentage	5.00%
Redeemable Noncontrolling Interest, Equity, Preferred, Carrying Amount	$ 1,000	$ 1,000
Outstanding Partnership Units held by Third Parties	1	1
Par or Stated Value Per Share	$ 1,000,000
Preference Or Annual Distribution Rate	$ 50,000
Cumulative Redeemable Preferred Unit [Member]
Redeemable Noncontrolling Interest Units Table [Abstract]
Outstanding Partnership Units held by Third Parties	9,000,001	10,400,001