Notes Payable, Unsecured Notes and Credit Facility (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
Notes Payable, Unsecured Notes and Credit Facility
Total notes payable and unsecured notes	$ 6,157,509,000		$ 6,029,998,000
Credit Facility	0		0
Total mortgage notes payable, unsecured notes and Credit Facility	6,157,509,000		6,029,998,000
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	2,450,000,000	[1]	2,600,000,000	[1]
Total notes payable and unsecured notes	2,700,000,000
Amount of debt discount	4,889,000		5,291,000
Term Loan
Notes Payable, Unsecured Notes and Credit Facility
Variable rate notes	250,000,000		0
Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	2,408,940,000	[2]	2,418,389,000	[2]
Variable rate notes	1,048,569,000		1,011,609,000
Total notes payable and unsecured notes	3,253,456,000
Amount of debt premium	102,254,000		120,684,000
Credit Facility
Notes Payable, Unsecured Notes and Credit Facility
Credit Facility	$ 0		$ 0

[1] Balances at June 30, 2014 and December 31, 2013 exclude $4,889 and $5,291 of debt discount, respectively, as reflected in unsecured notes, net on the Company’s Condensed Consolidated Balance Sheets.

[2] Balances at June 30, 2014 and December 31, 2013 exclude $102,254 and $120,684 of debt premium, respectively, as reflected in mortgage notes payable on the Company’s Condensed Consolidated Balance Sheets.