Notes Payable, Unsecured Notes and Credit Facility (Details 3) (USD $) In Thousands, unless otherwise specified																						9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Secured notes	Sep. 30, 2014 Secured notes Notes payable maturing in 2014	Sep. 30, 2014 Secured notes Notes payable maturing in 2015	Sep. 30, 2014 Secured notes Notes payable maturing in 2016	Sep. 30, 2014 Secured notes Notes payable maturing in 2017	Sep. 30, 2014 Secured notes Notes payable maturing in 2018	Sep. 30, 2014 Secured notes Notes payable maturing in 2019	Sep. 30, 2014 Secured notes Notes Payable Maturities 2020 [Member]	Sep. 30, 2014 Secured notes Notes Payable Maturities 2021 [Member]	Sep. 30, 2014 Secured notes Notes payable maturing in 2022	Sep. 30, 2014 Secured notes Notes payable maturing in 2023	Sep. 30, 2014 Secured notes Notes payable with maturities after 2023	Sep. 30, 2014 Unsecured notes	Sep. 30, 2014 Unsecured notes Notes payable maturing in 2016	Sep. 30, 2014 Unsecured notes Notes payable maturing in 2017	Sep. 30, 2014 Unsecured notes Notes Payable 6.100 Percent Maturities 2020	Sep. 30, 2014 Unsecured notes Notes Payable 3.625 Percent Maturities 2020	Sep. 30, 2014 Unsecured notes Notes payable maturing in 2021	Sep. 30, 2014 Unsecured notes Term Loan	Sep. 30, 2014 Unsecured notes Term Loan LIBOR	Sep. 30, 2014 Unsecured notes Notes payable maturing in 2022	Sep. 30, 2014 Unsecured notes Notes payable maturing in 2023	Sep. 30, 2014 Unsecured notes Notes Payable 2.850 Maturities 2023
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments			$ 199,707	$ 4,641	$ 17,871	$ 19,036	$ 20,257	$ 19,646	$ 7,145	$ 6,205	$ 5,985	$ 6,352	$ 6,596	$ 85,973
Mortgage notes payable and unsecured notes	$ 6,153,118	$ 6,029,998	$ 3,253,411		$ 586,703	$ 16,255	$ 710,491	$ 76,930	$ 658,475	$ 50,824	$ 27,844			$ 1,125,889	$ 2,700,000	$ 250,000	$ 250,000	$ 250,000	$ 400,000	$ 250,000	$ 250,000		$ 450,000	$ 350,000	$ 250,000
Stated interest rate of unsecured notes (as a percent)																5.75%	5.70%	6.10%	3.625%	3.95%			2.95%	4.20%	2.85%
Debt instrument variable rate																						LIBOR
Debt instrument, basis spread on variable rate (as a percent)																						1.45%