Scheduled Payments and Maturities of Mortgage Notes Payable and Unsecured Notes Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	$ 3,633,125		$ 4,068,417
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 4.323 Percent Maturities 2012
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	4.323%	[1]
Note Payable Maturities 2013
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	4.95%
Note Payable Maturities 2014
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.375%
Notes Payable Maturities 2016
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.75%
Notes Payable Maturities 2017
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	5.70%
Notes Payable Maturities 2020
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	6.10%
Notes Payable Maturities 2021
Debt Instrument [Line Items]
Stated interest rate of unsecured notes	3.95%
Secured notes payments
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	188,478	[2]
Secured notes payments | Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	13,675	[2]
Secured notes payments | Note Payable Maturities 2013
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	13,287	[2]
Secured notes payments | Note Payable Maturities 2014
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	14,098	[2]
Secured notes payments | Notes Payable Maturities 2015
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	11,975	[2]
Secured notes payments | Notes Payable Maturities 2016
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	12,605	[2]
Secured notes payments | Notes Payable Maturities 2017
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	13,496	[2]
Secured notes payments | Notes Payable Maturities 2018
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	14,330	[2]
Secured notes payments | Notes Payable Maturities 2019
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	2,597	[2]
Secured notes payments | Notes Payable Maturities 2020
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	2,768	[2]
Secured notes payments | Notes Payable Maturities 2021
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	2,952	[2]
Secured notes payments | Notes Payable Maturities Thereafter
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	86,695	[2]
Secured notes
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	1,813,646
Secured notes | Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	14,806
Secured notes | Note Payable Maturities 2013
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	223,473
Secured notes | Note Payable Maturities 2014
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	33,100
Secured notes | Notes Payable Maturities 2015
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	406,019
Secured notes | Notes Payable Maturities 2017
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	18,300
Secured notes | Notes Payable Maturities 2019
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	610,813
Secured notes | Notes Payable Maturities Thereafter
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	507,135
Unsecured notes
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	1,631,001
Unsecured notes | Notes Payable 5.500 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	104,400
Unsecured notes | Notes Payable 6.125 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	201,601
Unsecured notes | Notes Payable 4.323 Percent Maturities 2012
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	75,000
Unsecured notes | Note Payable Maturities 2013
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	100,000
Unsecured notes | Note Payable Maturities 2014
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	150,000
Unsecured notes | Notes Payable Maturities 2016
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	250,000
Unsecured notes | Notes Payable Maturities 2017
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	250,000
Unsecured notes | Notes Payable Maturities 2020
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	250,000
Unsecured notes | Notes Payable Maturities 2021
Debt Instrument [Line Items]
Total mortgage notes payable, unsecured notes and Credit Facility	$ 250,000

[1] The weighted average interest rate for the swapped unsecured notes as of December 31, 2011.

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