Senior Unsecured Notes and Secured Debt (Details)	9 Months Ended				9 Months Ended
	Sep. 30, 2013 USD ($)		Oct. 07, 2013 USD ($)	Dec. 31, 2012 USD ($)	Sep. 30, 2013 Senior Unsecured Notes [Member] USD ($)		Sep. 30, 2013 Secured Debt [Member] USD ($)		Sep. 30, 2013 Canadian Denominated Unsecured Term Loan [Member] USD ($)	Sep. 30, 2013 Canadian Denominated Unsecured Term Loan [Member] CAD	Sep. 30, 2013 Unsecured Line of Credit Term Loan [Member] USD ($)
Principal payments due on debt obligations
2013	$ 375,866,000				$ 300,000,000	[1],[2]	$ 75,866,000	[1],[3]
2014	326,307,000				0	[1],[2]	326,307,000	[1],[3]
2015	896,340,000	[4]			493,072,000	[1],[2],[4]	403,268,000	[1],[3],[4]
2016	1,584,127,000				1,200,000,000	[1],[2]	384,127,000	[1],[3]
2017	791,845,000				450,000,000	[1],[2]	341,845,000	[1],[3]
Thereafter	5,509,628,000				3,975,118,000	[1],[2]	1,534,510,000	[1],[3]
Totals	9,484,113,000				6,418,190,000	[1],[2]	3,065,923,000	[1],[3]
Senior Unsecured Notes and Secured Debt (Textual) [Abstract]
Notes, annual stated interest rates, Minimum					2.25%		1.00%
Notes, annual stated interest rates, Maximum					6.50%		9.10%
Interest rate			4.50%						2.67%	2.67%	1.53%
Senior unsecured notes issued amount			400,000,000
Senior unsecured notes	6,395,638,000			6,114,151,000					243,072,000	250,000,000	500,000,000
Secured debt	3,115,862,000			2,336,196,000
Carrying values of properties securing the debt	$ 6,336,955,000
Interest Rate margin	1.175%								1.45%	1.45%	1.35%
Debt instrument maturity date	Mar. 31, 2017								Jul. 27, 2015	Jul. 27, 2015	Mar. 31, 2016
Loan Extension Period	2 years 0 months

[1] (1) Amounts represent principal amounts due and do not include unamortized premiums/discounts or other fair value adjustments as reflected on the balance sheet.

[2] (2) Annual interest rates range from 2.25% to 6.5%, excluding the Canadian denominated unsecured term loan discussed in footnote 4 and the $500,000,000 unsecured term loan discussed below.

[3] (3) Annual interest rates range from 1.0% to 9.1%. Carrying value of the properties securing the debt totaled $6,336,955,000 at September 30, 2013.

[4] (4) On July 30, 2012, we completed funding on a $250,000,000 Canadian denominated unsecured term loan (approximately $243,072,000 USD at exchange rates on September 30, 2013). The loan matures July 27, 2015 (with an option to extend for an additional year at our discretion) and bears interest at the Canadian Dealer Offered Rate plus 145 basis points (2.67% at September 30, 2013).