Schedule III - Real Estate and Accumulated Depreciation (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Real estate:
Balances at beginning of year	$ 10,730,089	$ 9,756,927	$ 9,416,188
Acquisition of real estate and development and improvements	1,941,091	1,049,723	377,354
Disposition of real estate	(148,752)	(21,737)	(61,139)
Balances associated with changes in reporting presentation	110,195	(54,824)	24,524
Impairments	(7,878)
Balances at end of year	12,624,745	10,730,089	9,756,927
Accumulated depreciation:
Balances at beginning of year	1,449,579	1,226,122	1,015,263
Depreciation expense	302,332	294,480	254,799
Disposition of real estate	(32,942)	(5,705)	(27,123)
Balances associated with changes in reporting presentation	20,749	(65,318)	(16,817)
Balances at end of year	$ 1,739,718	$ 1,449,579	$ 1,226,122