Schedule III-Real Estate And Accumulated Depreciation (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Changes in real estate
Balance at beginning of year	$ 8,890,064,000	$ 8,257,100,000	$ 8,201,789,000
Property acquisitions	2,276,308,000	703,721,000	16,059,000
Improvements	162,875,000	97,099,000	92,117,000
Retirements/disposals/deconsolidation	(182,096,000)	(167,856,000)	(52,865,000)
Balance at end of year	11,147,151,000	8,890,064,000	8,257,100,000
Aggregate cost of land, buildings and improvements, before depreciation, for Federal income tax purposes	7,800,000,000
Changes in accumulated depreciation, exclusive of amounts relating to equipment, autos, and furniture and fixtures
Balance at beginning of year	916,293,000	738,422,000	546,545,000
Depreciation for year	245,421,000	209,472,000	210,436,000
Retirements/disposals/deconsolidation	(25,111,000)	(31,601,000)	(18,559,000)
Balance at end of year	$ 1,136,603,000	$ 916,293,000	$ 738,422,000