Significant Accounting Policies (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Noncontrolling interests:
Balance	$ 6,822,632
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized (loss) gain on derivative hedge agreements	(7,533)	7,070
Net loss reclassified from accumulated other comprehensive loss into earnings	2,697	1,511
Currency translation adjustments	13,733	1,048
Changes in available-for-sale securities and other	479	(184)
Purchase and dispositions of noncontrolling interests, net	6,130
Balance	6,864,281
Noncontrolling Interests
Noncontrolling interests:
Balance	973,226	982,486
Net income attributable to noncontrolling interests after preferred distributions and income attributable to redeemable noncontrolling interests in consolidated properties	57,650	47,559
Distributions to noncontrolling interest holders	(77,436)	(59,825)
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized (loss) gain on derivative hedge agreements	(1,236)	959
Net loss reclassified from accumulated other comprehensive loss into earnings	392	218
Currency translation adjustments	1,932	127
Changes in available-for-sale securities and other	72	(25)
Other comprehensive income (loss)	1,160	1,279
Adjustment to limited partners' interest from change in ownership in the Operating Partnership	(67,226)	(2,647)
Units issued to limited partners	84,910
Units exchanged for common shares	(911)	(2,521)
Long-term incentive performance units	12,485	11,422
Purchase and dispositions of noncontrolling interests, net	6,130
Balance	$ 989,988	$ 977,753