Changes in Total Real Estate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Real Estate and Accumulated Depreciation [Line Items]
Balance, beginning of period	$ 8,661,211	$ 8,360,091	$ 8,002,487
Acquisitions, construction costs and improvements	861,626	475,211	493,196
Dispositions, including impairment loss on planned dispositions	(234,341)	(174,091)	(135,592)
Balance, end of period	$ 9,288,496	$ 8,661,211	$ 8,360,091