Significant Accounting Policies (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Noncontrolling interests:
Balance, at beginning of period			$ 5,544,288
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized (loss) gain on interest rate hedge agreements	(8,587)	(7,740)	3,105	(19,023)
Net loss on derivative instruments reclassified from accumulated other comprehensive income into interest expense	5,138	3,824	10,252	7,768
Currency translation adjustments	(65,453)	8,754	(21,511)	30,653
Changes in available-for-sale securities and other	(666)	25,713	23,869	27,954
Balance, at end of period	7,130,599		7,130,599
Noncontrolling interests
Noncontrolling interests:
Balance, at beginning of period	1,215,628	771,152	894,622	802,972
Net income attributable to noncontrolling interests after preferred distributions and income attributable to redeemable noncontrolling interests in consolidated properties	42,308	44,088	175,318	83,029
Distributions to noncontrolling interest holders	(61,107)	(49,993)	(119,205)	(120,386)
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized (loss) gain on interest rate hedge agreements	(1,395)	(1,294)	1,006	(3,194)
Net loss on derivative instruments reclassified from accumulated other comprehensive income into interest expense	858	647	1,716	1,318
Currency translation adjustments	(10,957)	1,489	(3,433)	5,228
Changes in available-for-sale securities and other	(138)	4,334	3,819	4,677
Other comprehensive income (loss)	(11,632)	5,176	3,108	8,029
Adjustment to limited partners' interest from (decreased) increased ownership in the Operating Partnership	(7,547)	(947)	156,299	(6,585)
Units issued to limited partners				202
Units exchanged for common shares	(2,600)	(3,712)	(4,018)	(5,923)
Purchase of noncontrolling interest and other	10,368	8,130	79,294	12,556
Balance, at end of period	$ 1,185,418	$ 773,894	$ 1,185,418	$ 773,894