Reconciliation of NOI to Net Income (Detail) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Segment Reporting Information [Line Items]
Net income	$ 43,192	$ 51,066	$ 73,728	$ 123,432
Indirect operating expenses, net of corporate income	7,701	7,849	14,729	15,080
Investments and investment management expense	1,341	1,047	2,532	2,086
Expensed acquisition, development and other pursuit costs	1,353	443	2,004	947
Interest expense, net	45,855	41,458	90,126	83,999
General and administrative expense	8,145	4,041	15,437	12,936
Equity in (income) loss of unconsolidated entities	(395)	(463)	(898)	(689)
Depreciation expense	62,894	57,317	124,154	113,250
Gain on sale of real estate assets	(7,675)	(21,929)	(7,675)	(72,220)
(Income) loss from discontinued operations	91	(35)	197	(1,813)
Net operating income	$ 162,502	$ 140,794	$ 314,334	$ 277,008