Notes Payable, Unsecured Notes and Credit Facility (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
Notes Payable, Unsecured Notes and Credit Facility
Total notes payable and unsecured notes	$ 6,493,278,000		$ 6,448,138,000
Credit Facility	0		0
Total mortgage notes payable, unsecured notes and Credit Facility	6,493,278,000		6,448,138,000
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	2,750,000,000	[1]	2,750,000,000	[1]
Total notes payable and unsecured notes	3,050,000,000
Amount of debt discount	6,491,000		6,735,000
Term Loan
Notes Payable, Unsecured Notes and Credit Facility
Variable rate notes	300,000,000		250,000,000
Secured notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	2,396,479,000	[2]	2,400,677,000	[2]
Variable rate notes	1,046,799,000		1,047,461,000
Total notes payable and unsecured notes	3,330,306,000
Amount of debt premium	75,544,000		84,449,000
Credit Facility
Notes Payable, Unsecured Notes and Credit Facility
Credit Facility	$ 0		$ 0

[1] Balances at March 31, 2015 and December 31, 2014 exclude $6,491 and $6,735 of debt discount, respectively, as reflected in unsecured notes, net on the Company’s Condensed Consolidated Balance Sheets.

[2] Balances at March 31, 2015 and December 31, 2014 exclude $75,544 and $84,449 of debt premium, respectively, as reflected in mortgage notes payable on the Company’s Condensed Consolidated Balance Sheets.