Mortgage Notes Payable, Unsecured Notes and Credit Facility (Detail) (USD $)	Sep. 30, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Notes payable and unsecured notes	$ 3,785,830,000		$ 4,068,417,000
Variable rate unsecured credit facility
Total mortgage notes payable, unsecured notes and unsecured credit facility	3,785,830,000		4,068,417,000
Fixed rate notes | Unsecured notes
Debt Instrument [Line Items]
Notes payable and unsecured notes	1,556,001,000	[1]	1,595,901,000	[1]
Fixed rate notes | Secured notes
Debt Instrument [Line Items]
Notes payable and unsecured notes	1,681,348,000	[2]	1,651,135,000	[2]
Variable rate notes | Unsecured notes
Debt Instrument [Line Items]
Notes payable and unsecured notes	75,000,000	[1]	225,000,000	[1]
Variable rate notes | Secured notes
Debt Instrument [Line Items]
Notes payable and unsecured notes	473,481,000		596,381,000
Unsecured notes
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and unsecured credit facility	1,631,001,000
Secured notes
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and unsecured credit facility	$ 1,680,327,000

[1] Balances at September 30, 2011 and December 31, 2010 exclude $1,952 and $2,269, respectively, of debt discount, and $185 and $1,509, respectively, for basis adjustments, as reflected in unsecured notes on the Company's Condensed Consolidated Balance Sheets.

[2] Balance at September 30, 2011 excludes $ 1,030 of debt premium as reflected in mortgage notes payable on the Company's Condensed Consolidated Balance Sheet.