Significant Accounting Policies (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Noncontrolling interests:
Balance			$ 6,893,089
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized (loss) gain on derivative hedge agreements	(4,378)	(8,555)	897	(5,450)
Net loss reclassified from accumulated other comprehensive loss into earnings	2,566	5,187	6,642	15,440
Currency translation adjustments	32,515	9,138	10,603	(12,374)
Changes in available-for-sale securities and other	(773)	16,573	(1,588)	40,442
Other comprehensive income (loss)			14,198
Balance	6,804,493		6,804,493
Noncontrolling Interests
Noncontrolling interests:
Balance	971,498	1,185,418	982,486	894,622
Net income attributable to noncontrolling interests after preferred distributions and income attributable to redeemable noncontrolling interests in consolidated properties	52,339	47,668	157,100	222,986
Distributions to noncontrolling interest holders	(60,197)	(62,149)	(180,104)	(181,354)
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized (loss) gain on derivative hedge agreements	(629)	1,327	111	2,333
Net loss reclassified from accumulated other comprehensive loss into earnings	369	517	955	2,233
Currency translation adjustments	4,676	2,716	1,518	(717)
Changes in available-for-sale securities and other	(111)	902	(228)	4,721
Other comprehensive income (loss)	4,305	5,462	2,356	8,570
Adjustment to limited partners' interest from change in ownership in the Operating Partnership	(8,841)	(38,715)	(19,422)	117,584
Units exchanged for common shares	(59)	(129,783)	(6,041)	(133,801)
Units Redeemed		(38,904)		(38,904)
Purchase of noncontrolling interests and other	16,629	10,367	39,299	89,661
Balance	$ 975,674	$ 979,364	$ 975,674	$ 979,364