Scheduled Payments and Maturities of Mortgage Notes Payable and Unsecured Notes Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	$ 3,986,416		$ 4,068,417
Secured notes payments
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	477,975	[1]
Secured notes payments | Notes Payable 6.625 Percent Maturities 2011
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	7,356	[1]
Secured notes payments | Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	15,508	[1]
Secured notes payments | Notes Payable 4.950 Percent Maturities 2013
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	15,134	[1]
Secured notes payments | Notes Payable 5.375 Percent Maturities 2014
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	16,031	[1]
Secured notes payments | Notes Payable Maturities 2015
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	13,867	[1]
Secured notes payments | Notes Payable 5.750 Percent Maturities 2016
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	14,690	[1]
Secured notes payments | Notes Payable 5.700 Percent Maturities 2017
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	15,568	[1]
Secured notes payments | Notes Payable Maturities 2018
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	16,498	[1]
Secured notes payments | Notes Payable Maturities 2019
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	2,588	[1]
Secured notes payments | Notes Payable 6.100 Percent Maturities 2020
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	2,761	[1]
Secured notes payments | Notes Payable 3.950 Percent Maturities Thereafter
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	357,974	[1]
Secured notes maturities
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	1,687,540
Secured notes maturities | Notes Payable 6.625 Percent Maturities 2011
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	7,213
Secured notes maturities | Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	14,661
Secured notes maturities | Notes Payable 4.950 Percent Maturities 2013
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	318,045
Secured notes maturities | Notes Payable 5.375 Percent Maturities 2014
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	33,100
Secured notes maturities | Notes Payable Maturities 2015
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	405,613
Secured notes maturities | Notes Payable 5.700 Percent Maturities 2017
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	18,300
Secured notes maturities | Notes Payable Maturities 2019
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	651,973
Secured notes maturities | Notes Payable 3.950 Percent Maturities Thereafter
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	238,635
Unsecured notes maturities
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	1,820,901
Unsecured notes maturities | Notes Payable 6.625 Percent Maturities 2011
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	39,900
Unsecured notes maturities | Notes Payable 5.687 Percent Maturities 2011
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	150,000
Unsecured notes maturities | Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	104,400
Unsecured notes maturities | Notes Payable 6.125 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	201,601
Unsecured notes maturities | Notes Payable 4.352 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	75,000
Unsecured notes maturities | Notes Payable 4.950 Percent Maturities 2013
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	100,000
Unsecured notes maturities | Notes Payable 5.375 Percent Maturities 2014
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	150,000
Unsecured notes maturities | Notes Payable 5.750 Percent Maturities 2016
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	250,000
Unsecured notes maturities | Notes Payable 5.700 Percent Maturities 2017
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	250,000
Unsecured notes maturities | Notes Payable 6.100 Percent Maturities 2020
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	250,000
Unsecured notes maturities | Notes Payable 3.950 Percent Maturities Thereafter
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	$ 250,000
Notes Payable 6.625 Percent Maturities 2011
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	6.625%
Notes Payable 5.687 Percent Maturities 2011
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.687%	[2]
Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.50%
Notes Payable 6.125 Percent Maturities 2012
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	6.125%
Notes Payable 4.352 Percent Maturities 2012
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	4.352%	[2]
Notes Payable 4.950 Percent Maturities 2013
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	4.95%
Notes Payable 5.375 Percent Maturities 2014
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.375%
Notes Payable 5.750 Percent Maturities 2016
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.75%
Notes Payable 5.700 Percent Maturities 2017
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.70%
Notes Payable 6.100 Percent Maturities 2020
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	6.10%
Notes Payable 3.950 Percent Maturities Thereafter
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	3.95%

[1] Secured note payments are comprised of the principal pay downs for amortizing mortgage notes.

[2] The weighted average interest rate for the swapped unsecured notes as of June 30, 2011.