Mortgage Notes Payable, Unsecured Notes, Credit Facility and Cancelled Credit Facility (Detail) (USD $)	Dec. 31, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Total notes payable and unsecured notes	$ 3,633,125,000		$ 4,068,417,000
Credit Facility and Cancelled Credit Facility
Total mortgage notes payable, unsecured notes and Credit Facility	3,633,125,000		4,068,417,000
Unsecured notes
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	1,631,001,000
Secured notes
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	1,813,646,000
Fixed rate notes | Unsecured notes
Debt Instrument [Line Items]
Total notes payable and unsecured notes	1,556,001,000	[1]	1,595,901,000	[1]
Fixed rate notes | Secured notes
Debt Instrument [Line Items]
Total notes payable and unsecured notes	1,528,783,000	[2]	1,651,135,000	[2]
Variable rate notes | Unsecured notes
Debt Instrument [Line Items]
Total notes payable and unsecured notes	75,000,000	[1]	225,000,000	[1]
Variable rate notes | Secured notes
Debt Instrument [Line Items]
Total notes payable and unsecured notes	$ 473,341,000		$ 596,381,000

[1] Balances at December 31, 2011 and December 31, 2010 exclude $1,802 and $2,269 respectively of debt discount, and $11 and $1,509, respectively for basis adjustments, as reflected in unsecured notes on the Company's Consolidated Balance Sheets.

[2] Balance at December 31, 2011 includes $962 of debt premium as reflected in mortgage notes payable on the Company's Consolidated Balance Sheets.