Significant Accounting Policies (Details 4) (USD $) In Thousands, unless otherwise specified			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Noncontrolling Interests	Jun. 30, 2012 Noncontrolling Interests	Jun. 30, 2013 Noncontrolling Interests	Jun. 30, 2012 Noncontrolling Interests	Jun. 30, 2013 7.5% Cumulative Redeemable Preferred Units Noncontrolling Interests
Noncontrolling Interests:
Dividend rate on cumulative redeemable preferred units (as a percent)							7.50%
Balance	$ 6,806,247	$ 6,893,089	$ (931)	$ (619)	$ (877)	$ (59,000)
Net Income (loss) attributable to noncontrolling nonredeemable interests			23	(15)	26	(2)
Distributions to noncontrolling nonredeemable interestholders			(119)		(178)	(191)
Purchase of noncontrolling interests and other			(2)			58,559
Balance	6,806,247	6,893,089	(1,029)	(634)	(1,029)	(634)
Noncontrolling interests redeemable at amounts in excess of fair value			$ 0		$ 0